You are going to have to accept the emotional consequences of your requests. What you are asking us for is a polite way to tell your mother to get out which is saying, "How can I get what I want with out having to deal with the consequences ie emotional guilt, blackmail, and pain?" The answer, you can't. You either stiffen your spine, and know that no matter what you do, there's going to be fallout, or you endure the situation that is.
You can't have it both ways. You must choose what is more important to you, your child and husband, or your mother. Doing nothing about it is making a decision as well. You can do it and it will be worth it in many ways. You are not being unreasonable, you are not being cruel, you are protecting your family. She will pitch a fit and try and make you feel guilty, don't let her. She doesn't want to change. Change would mean she would have to accept the consequences of her financial decisions. That she might have to accept that she's failed.