I'm pulling for you, Sally. Taking on extra burden often snowballs but as long as your sister is helping herself, too, you are being a great person. I often find myself doing all the work when I start to help someone. Then I step back and get upset. I hope this is not the case for you.
I went out and bought my son in law who totaled his car, got a DUI, and lost his job recently an entire Thanksgiving dinner to make for him and my grandkids. I barely got a thank you. Then he walked to the local store and came home with a carton of cigarettes. I realized that a pack a day cost him $183. So, I stopped being so generous. Not to judge but maybe that $183 would have gone for the food they needed instead of cigs had I not helped out.