Oh my, I sympathise with you completely. You are doing the right thing, and don't let anybody tell you that you aren't. Your MIL should be thankful that she has someone like you in her family that is prepared to help her out to such an extent in problems such as this. She needs to remember that kind people like you don't grow on trees!

I really hope that your MIL addresses her drink problem. Has your husband tried to talk to her about this privately? Not to be rude or anything, but words may have a little more depth to them if they come from her son, and if he explains how her actions are upsetting him and those close to him, then surely she must see sense.