Be your own person and fight for yourself. But also, stop talking to her about it. Other people have other agendas for us, even if they mean well. But stop all the background noise from one or others. Get some calm moments for yourself and make your own decisions on which direction you want to go. You need to go through the surgery by yourself and the recovery and weight loss management yourself. So don't give your energy and power away, but save it for yourself to find what is what you want for yourself.
Best of luck