Wobbler's or EPM. She may not have been born with it. If she isn't balanced enough to carry a rider at a canter, I wouldn't be using her on trails at a walk or trot. If it is EPM it's $700/mo for 3 months to treat and that doesn't guarantee a cure. No matter how cheap she is now, you will be seeing vet bills in the future.
A neurological problem isn't "just one of those things". It is a serious condition. If a horse isn't balanced enough to carry itself, how can you expect it to carry a rider? Sounds like someone is trying to pass of their problems to the first taker.