need help with weight gaining

I have a 29 yr old QH mare i've had her since i was 7yrs and i'm 20 now, so i've had her a good while me and my husband had a friend boarding her for us while out of town working. She was not under weight at this time when we got back you could see her spine hips ribs everything. we have tried different things and nothing has seemed to work.We tried One and Only for horses, its seem to work at first but after about a week it no longer worked. We have her on All stock at this time, plus bread. Shes been wormed so thats not the problem she has a clean bill of health from vet .PLEASE I REALLY NEED HELP!!!..She maybe older then me but she's my baby

[Davina73]

She probably was not in good hands.  Check her teeth, they may need floating.