I think your feasible options are to retire the horse on your own dime if she’s pasture sound WITHOUT meds, or euthanize her. I wouldn’t pursue riding her or attempting to re-home her, from what you’ve described.
However, I think it’s important to note that while your experience sucks balls, it’s not some crazy anomaly. I had an old trainer tell me years ago that he estimated that about 60-70% of OTTBs come off the track unsound to the point that they can’t be used for even low-level competitive riding. And that often, the unsoundness is not obvious at first, especially if the horse has had a break since racing. This gels pretty well with my unscientific observations in the 20 years since. So I really think that if you buy an OTTB, you need to be prepared for this outcome, and have a plan.
This isn’t a criticism of the OP, but I feel like I see so many people buying OTTBs for cheap, and expecting some sort of fairytale. It’s a big risk, especially if you don’t have 5 acres out the back where you can just let them be for 10 years if they won’t stay sound.
OP, if she is completely pasture sound without any painkillers, and copes ok with living out, you could find a place to retire her. That’s what I did with my guy, I found a place for about $350/month, and he seems to love it. But if she isn’t both of those things, I’d euthanize her without hesitating. Quality of life is everything.