How can I have an adult relationship with my mom when she acts worse than my toddler?

Good for you for stating all this. Now all you have to do is detach! It is not fair to your own 'stable marriage' to give this much concern and energy to someone who does not respect you. Try to get over the mourning for the relationship you wish you could have had. Let her accuse all she wishes and meanwhile go on with your life. If she confronts you on it again, simply say 'I am sorry that I can't please you but it just isn't working' or the less said the better probably. Just be busy when she tries to do something with the children or asks you to come. It is truly up to you to manipulate yourself out of this mess. But I know you can do it.