Sister's cat very ill/hurt, vet is stumped

Some background: my sister's cat Starling was abused as a kitten, resulting in a broken tail, malformed ribs, and very bad teeth. The shelter thought she had been kicked. She's six, was at the shelter since she was a kitten, and my sister adopted her about 18 months ago.

Starling came down with a mystery ailment a little after Thanksgiving, almost immediately after my sister had some friends stay over at her apartment. She got dizzy while jumping down from the couch, and couldn't get her balance after that. She would also walk with her head tilted to the side, stumbling all over the place. My sister took her to the vet, who had no idea what the issue could be but gave my sister some ear drops in case it was ear wax build up. Starling started acting different at this time, too. She was normally shy and would hide under my sister's bed when I came by to feed her and give her drops, but she started laying on top of my sister's bed constantly, even allowing me to lay down next to her and give her the drops without issue. My sister went to my parents' house for Christmas and took the cats with her, and I hadn't heard anything else until today. My sister says that Starling took a turn for the worst and is having to be fed with a syringe. The vet is recommending a neuro consult and an mri, but that is prohibitively expensive for my 23-year-old sister who just moved to Chicago a few months ago. I'm going to feed Starling tomorrow during the day, and my sister wants to discuss putting Starling down when she gets home from work. I'm not really sure what I'm asking here, but if anyone has dealt with something that sounds similar I'd really appreciate some insight.

The head tilting and balance issues could be caused by an inner ear infection or from Vestibular Syndrome, but the 2nd issue usually goes away fairly quickly.  Here is a thread on it where this cat also required syringe feeding, which isn't the norm.  http://www.thecatsite.com/t/234663/barney-has-feline-vestibular-syndrome

THIS thread is about a cat that actually had an inner ear infection that wasn't at first detected:  http://www.thecatsite.com/t/252746/cat-with-possible-vestibular-balancd-problems

I sincerely hope this issue with Starling is one that can easily be resolved and doesn't result in her losing her life.  I

I went to feed Starling just now, and it looks really bad. She is curled up in a cubby hole in my sister's closet, purring constantly trying to comfort herself. She growls/moans at the slightest movement, and her face and front legs are wet from either constantly drooling, food she couldn't swallow, or licking in an attempt to feel better. It smells pretty bad in there, too, like a cast after a few weeks.

The vet has run blood tests and said that the only thing left was an mri. According to my mom, who took him to the vet, they didn't sound too hopeful that an mri would be successful.