Morbidly obese stepchild

Well, you can call CPS and then be prepared to be divorced or you can become this child's friend and mentor. You can have her help you cook and teach her how to cook in a healthy manor. When she comes over, have her go out for walks with you or suggest other activities that means that she gets up off her butt and moves around. Have you talked to her about it? Maybe she you can enlist her help to help you lose weight or get more active. Take her grocery shopping and let her see you studying labels, let her help in planning healthy menus. Obviously the other adults in her life are oblivious, do an end run around. When she comes to visit, for snacks have baby carrots and other veggies. If you get along with her, play a game - scrabble then suggest a nice walk before a 2nd game or before starting dinner, become her friend, kids can be cruel, my guess is she needs some friends.

What does her pediatrician say? I know they probably aren't allowed to talk to you, but your husband should be in on those conversations. Try to do "fun" exercise. Swimming is great for the body, is there an inside community pool close by? A trampoline is also great exercise (I used to use mine as a workout all the time, wish I still had it). Try not to have any "snacks" in the house when she's around. No chips, cookies, sodas. Just stuff that's good for you. But, for contacting social services... That's a tough call... The parents are likely to just resent you for it. And the daughter might be taken away from both of them, making things worse. Best of luck to you!