oh, such a shame to hear that.. have they checked to make sure theres no wood slivers in the puncture? sometimes that will act the same way, if shes still putting full weight on it, id hang on and try to keep her on antibiotics as long as shes enjoying herself for now, I did have a horse that embedded wood in her tendon area, xrays didn't show it, and it drained and drained, almost six weeks, same as yours , off and on painful and swelled, then it would leak pus and was really ugly, vets were fairly sure it was a joint involved, but i was out there and saw a black colored odd shape, i thought it was a bone chip, when i pulled it, it was a sliver of wood that had went in and lined up with her tendon, up to that point, it was a puncture wound, but once the stick was out, it closed up, and she was fine.. I hope the best for your mare, shes lucky to have you , I would do exactly what you are , try to squeak out some time as long as shes comfortable..