Oh wow. I'm glad you found out the problem, poor girl. She must be in pain. I always like to check teeth now before buying...I had someone con me into a "two or three" (what they said when I asked her age at first) year old doe that when I got her home, just didn't seem right...looked at her teeth and she looked a good deal older...I called them up and said I was not happy with her, they let me take her back, and when I complained about how she really wasn't holding her weight well, they said "Well, you know, she's really old..." Grr.
Hopefully you can get your girl's teeth fixed up and find a good feed for her.
Sheesh.... That sounds exactly like what has happened here. This doe is having problems holding her weight also. We have had to put her on a special diet with her teeth the way they are or she would just about starve. She is gaining weight now though.
I'm never one to tell someone to use a feed that is not breed specific but I've had more then one goat person tell me they use Senior Horse feed on their senior goats. I have not tried it myself.
I use Purina Senior feed on an old horse. It is a soft pellet feed with a small amount of molasses and a higher fat content. It has done wonders for my horse. I have a couple of goats that grab a few bites each day and they're fine.