Overweight and scheduled mitral valve replacement

My 62-year-old mother had a TEE today and was reported that she has a large blood clot in her heart. Has been on coumadin for many years. She weighs 325 pounds and has been told for years now that she needs to lose weight to eventually have a mitral valve replacement because her MD states "no surgeon will touch you until you are at least 285 pounds." With the TEE results today however they are pushing for the mitral valve replacement as soon as possible even given the risks because of the size and location of the blood clot. It appears that her risk of having a PE or CVA has greatly increased so much as that they are willing to risk doing such a serious procedure as is the mitral valve replacement. Of course many concerns here....risks? probability of surviving the surgery itself? extensive recovery time due to weight? Should she really even have the heart surgery and risk her life during it however she could have a stroke or PE at any time without the surgery. Lots of information overload. Would like any sort of feedback. Thanks so much for your time.