This whole thing sounds rather odd to me. I feel very sorry for your dog. She needs help, obviously, and it's your responsibility to make her quality of life better. I would suggest you do everything you can to help her lose weight, take her for proper walks, and generally, do all you can do, and more, to make her be more healthy and fit. Find a way to stop the overfeeding family member and find a way to get her in for some immediate vet care. You have to take care of her. She can't do it herself

At the risk of saying something I shouldn't, I'll leave it at that