I can truly feel your pain because I had to officially retire my Beau this year at the young age of 14. He came up with pretty bad arthritis in his back right leg, in the stifle and the hock. The vet said injections would only serve to keep him comfortable, but wouldn't bring him back to running, or hardly even regular light riding.
I had to hold back tears many times since then, as it was really, really hard to hang up his bridle (considering I finally graduated from 8 years of college for my optometry degree), but I know it was the right decision.
Good luck with your horse, and I hope you don't have to retire her, but make the right decision when the time comes. Horses are way too giving. They'll still run a pattern if you ask, even though they are in pain. (I know my guy would race at it if I were to hop on him tonight and ask ..... he's loves it.)
∞•*˚ Βгįťţαňγ ˚*•∞
It is not enough to know how to ride; one must know how to fall.