Oh my goodness, what a cutie pie she is!!
When you say she lost her coat, did she lose it and be bald?? Or did she just lose some of the longer hair? I had a yorkie/chi foster who had short hair interspersed with long hair and it often looked wispy. I usually just kept it clipped short as it looked neater to me.
If she is actually losing hair as in going bald, I would definitely be thinking of something like Cushings....or Alopecia X which is also known as Pseudo Cushings. I had a foster pup with that. Here is a thread about him...and his pics are in there somewhere...
http://www.yorkietalk.com/forums/sic...hair-loss.html