Not that I'm any sort of expert but...
I would avoid lunging her til whatever it is has been identified and fixed (if possible). If you're determined to work her (I'd leave it til after everything has been cleared up myself, there's no rush) try ground driving her and working in straight lines. Just take things nice and slow (training wise) and don't worry too much about collection, her muscles will need to develop for that. How old is she, may I ask?
A vet will help localise any leg pain through flexion tests and should be able to perform x-rays to identify any arthritis, bone spurs etc. A chiropractor would also be great to get out to pinpoint and fix any tightness and alignment issues.
If it is a joint problem then it's a came of managing it rather than fixing it but there are some decent supplements out there and you can get joint injections - none of that stuff is cheap I'm afraid, and she may never be sound. Arthritis is a b****
But I'd wait to see what the vet says.
Sadly this stuff isn't uncommon with OTTBs, racing places great stresses on developing musculoskeletal structures. Posted via Mobile Device