I don’t think you’re seeing this clearly, at all yet. Your mother is very, in various ways abusive to you and clearly the cause of a lot of your issues, especially all this “failure to launch.” It’s almost a self imposed dependency on this monster who abuses you physically, sexually, verbally and emotionally. You could get a job, rent a room and live on your own right now if you wanted to, probably. What is actually stopping you from doing that?
She has mental health issues, but that’s not your problem to handle. You should listen to your therapist. You need to consider yourself, your mental health and your well being before anything else, especially dear old mom, who’s been the cause of much of your stunted growth and pain.
It’s time to dedicate yourself to becoming independent and moving out. Your therapist is itching to help you do this.