** I am not a veterinarian** But I still know a thing or two...
Part 1
*I've underlined and bolded the symptoms in my ewe, and halfway down there is a list of the treatments that I used. With the vital treatments in red.

Story time: 1/25/2016
  So while I was having a blast, enjoying my first week at UMass Amherst, my ewe Bluebelle (currently a yearling, will be 2 this spring 2016) went and got sick.
  My sister messaged me on Friday saying "SHEEP EMERGENCY CALL ME". I called her, and we chatted about how BB is doing. She tells me, that she is shaking, stiff-legged, and keeps falling. Also that she is drooling and tilting her head. My thoughts immediately go to listeriosis. I ask if she has been off feed, how her stool is, if she has miscarried. It turns out that BB has been acting normal up until today; when Liv went out to feed and found her leaning up against the fence. Liv immediately separated her, and gave her nutridrench, yogurt and water... I instruct her to call our vet, and have her come over asap.
  I travel home the next day, and take a look at my babe. She is just as described, shaky, stiff, and easily started. The paralysis in her face was very mild, and she could still walk (stumble). She could even eat a bit of hay. Our vet had given her penicillin and banamine (to treat her for the worst case scenario  listeriosis), She was not positive of what exactly was effecting BB. Her symptoms were common for many bad illnesses.
  Later that day I learned that in the morning, BB had had a seizure, she fell to the ground on her side and shook. After hearing this, my thoughts immediately jumped away from listeriosis and instead to a mineral deficiency. Specifically hypocalcemia, which I remembered causes seizures in the death strokes... But we were treating her for listeriosis, so maybe it was just the medicine working to kill the bacteria in her brain? 
  After a night of fitful sleep, I went out at noon to re-evaluate. Liv and I dosed her with 3ml penicillin, and 1ml banamine (both IM); we also drenched her with nutri-drench, yogurt, and water... A minute after the complete drenching +shots, I noticed BB shaking her head (essentially a mild seizure), her lips , ears, and eyes flapped and twitched. While she braced herself against the wall. She recovered and I finished feeding the rest of the animals. When I came back into the barn a few minutes later, I heard a splash, when I looked into the stall BB was full on seizing on the ground, with legs fully stretched and flailing. I went in and held her head, and talked her through it. She proceeded to have another full-on, and another semi- seizure in a span of 10 minutes... As I was helping her through the seizures, I knew this wasn't listeriosis. It was something much different, maybe the banamine was to blame? (shot of banamine, then 5 mins later, intense seizures? Can't be a coincidence)
  So I left her in a recumbent position (legs underneath her), and went inside to research. At first I was looking to see if banamine causes seizures in sheep (it has never before in my animals, but I just wanted to make sure). Turns out that it does when accidentally given in an artery. I am sure I did not hit an artery, so I kept looking. I knew a symptom of BB's was seizures, so I researched hypocalcemia [which I suspected earlier], not it. But somewhere on that deep dive, I came across hypomagnesaemia, low magnesium [grass tetany]. And BOOM, that was it. Grass tetany causes a stiff gait, tremors, excessive peeing, and near death - flailing seizures..
 I went back out to the barn to call our vet, whilst keeping an eye on BB in fear she may be already dead. She was not, but she was on the ground and seizing again... I called our vet and told her my new diagnosis. She said to give her CMPK and/or Epsom salts (magnesium oxide). Our CMPK drench was expired, but we had fresh epsom salts! It is recommended to give this IV, or Sub-Q for rapid treatment; but we only had oral. So I gave her 2oz of the expired CMPK D3 drench orally. Later on I mixed her a drench of 10g epsom salts, water, and molasses. We gave this to her at 5pm.
  For her continued care, she will receive 5g epsom salts per feeding (2x a day), nutri-drench, yogurt, and propylene glycol (to prevent toxemia).
 There is not great documentation if this kind of treatment works long term, and sheep often relapse. But as of now (approximately 62 hrs since first signs of tremors), she has no facial tremors, and her legs are beginning to be less stiff. If she makes it, I predict she will have moderate to severe brain damage, but hopefully she will not be in pain. 

What caused grass tetany in the middle of winter? 

• My theory is that due to all the weird and cold weather we have been having, it caused her to go off grain/hay for some time, which caused her already low* magnesium levels to plummet. She was low in the pecking order too, which didn't help her get the food she needed.  
• We have been feeding differently this year, usually we supplement with alfalfa when we are low on hay, but instead I have been using forage extender pellets. They work great, but obviously don't have the nutrient content of alfalfa. 

Treatment:

Friday (noon) 0hrs: 40-80ml nutri-drench, h20
3hr: 20ml yogurt, 20ml nutri-drench, h20, 3ml penicillin, 1ml banamine
6hr: 20ml yogurt, 40ml nutri-drench, 20ml h20
9hr: 20ml yogurt, 40ml nutri-drench, 20ml h20, 1ml banamine 
  (seizures)

Saturday
18hrs: 20ml yogurt, 20ml nutri-drench, 20ml h20
21hrs: 20ml yogurt, 20ml nutri-drench, 20ml h20
(noon) 24hrs: 20ml yogurt, 20ml nutri-drench, 20ml h20
3pm 27hrs: 20ml yogurt, 20ml nutri-drench, 20ml h20
6pm 30hrs: 20ml yogurt, 20ml nutri-drench, 20ml h20, 3 ml penicillin
9pm 33hrs: 20ml nutri-drench, 20ml h20
  (stopped yogurt, she was eating hay)

Sunday
42hrs: 20ml nutri-drench, 20ml h20
45hrs: 20ml nutri-drench, 20ml h20
(Noon) 48 hrs: 20ml nutri-drench, 20ml h20 , 3 ml penicillin, 1ml banamine
(4+seizures)
49hrs: 2oz CMPK D3 drench
53hrs: 10g epsom salt solution, 20ml nutri-drench, 20ml h20
57hr: 80ml propaline glycol
  *10grams a day of epsom salts is the max recommend for sheep. So continuing on I gave her 5g dissolved in water, twice a day*

Monday
noon: 20ml nutri-drench, 20ml h20

• You may notice that we were giving a ton of nutri-drench. This was because it is full of nutrients that would help cure any of the things we thought she had. Calcium (milk fever), magnesium (grass tetany), sugar/molasses/propylene glycol (pregnancy toxemia), thiamine (thiamine deficiency). Since we didn't know what she had, we decided to just hit all the bases. Also the vitamin D in it helps to calm them down. 

Part 2:
Update: (I got distracted and forgot I hadn't posted this, so it's now Oct 27 2016) lol

• Due to the stress of the seizures, and the amount of propylene glycol* we gave her, she did end up aborting her fetus. This occurred a few days after the multiple seizures. ​*Large doses of propylene glycol are known to cause spontaneous abortions in ewes, especially when they are in their 1 or 2nd trimester. 
• For the next week, I had my mom and sister continue giving her nutridrench every other day, and 5g epsom salts 2x a day with water.
• Bluebelle started looking brighter and more conscious. We slowly eased her off the heavy dose of epsom salts. She relapsed a little after a week, but was fixed with more salts. To keep her from relapsing again we gave her wetted alfalfa cubes sprinkled with a bit of the salts. Also we kept her separated from the other ewes since she still couldn't walk well. 
• For the next couple months we partnered her up with our old ewe Angel, and eased off the salts. Angel helped BB by encouraging her to eat and drink regularly, which helped her keep her magnesium levels normal. As the weather warmed up, we let them out to stretch their legs in the back yard, and BB jumped around with Angel like they were both lambs again.
• Overall, BB recovered extremely well, and even was well enough to go on pasture later in the summer, and is fat enough to be bred again this fall. We will be watching her closely to see if she has a relapse this winter; but things are looking really well at the moment. She does not seem to have any severe brain damage like I had predicted. Though she is definitely calmer then before, and a little more playful. 
• Conclusion: Bluebelle was definitely suffering from Grass Tetany. Even though it was a tough ride, there were no lasting effects, except a crack in her hoof wall. My theory is that such intense stress (almost dieing) showed up with a huge cleft in her hoof. Much like with rams how you can see changes in nutritional level, or stress in their horn ridges. If she was a ram, I think the horn would have become very brittle in that groove, and may have even broken.  

  I am very proud of how my family managed her care after I left, and I'm very happy with how Bluebelle persevered. She fought so hard for her life, and never gave up, even when other animals would've. Even if she doesn't turn out to be brood ewe material, I will still give her the loving forever home that she deserves. EDIT: Bluebelle ended up having a peaceful pregnancy, and delivered two healthy ewe lambs. The three of them were bought by a fiber artist on Cape Cod, and were companions to their own aged cheviot. :) 

Thanks for reading, and sorry again for taking so long to post! 
Until next time,
 - Isabelle