If you were to cut all financial support from her, would you be able to survive? Or would it just lower your standard of living? It is an important question because it is one of the main ways she legitimately enters your life and then feels she has a "stake" in the outcome.
I applaud your efforts to be independent. I would think that a gradual but progressive path towards total independence (which may require that you work part time, accept support from another source part time and/or change your standard of living even) would go a long way toward shutting down that pathway and allowing you to create other more constructive paths, if possible, with your mom-- like having fun together shopping or reading the same book to discuss together (how about Melody Beattie's Codependent No More for starters) or an outing, if possible?
I have several "disabilites" for which I seek various forms of outside help. Any one of them could have set up similar circumstances with my family had I sought their help. My family has money and it was often offered but always with strings attached. Even without the money complicating it, I found it was impossible to have a relationship with either my father or sister that wasn't codependent at their end. It eventually caused complete estrangement between us since there simply wasn't much left to say to each other once I learned how not to play the game.
Even from friends I have known, sometimes help isn't very helpful. I have changed a lot over the years (from therapy) and had to let go of friends who simply couldn't accommodate the changes from me -- they don't call that marvelous book "Courage To Heal" for a flimsy reason! There are reasons people come and go in our lives and I have learned to appreciate them all, whether they stay a while or not.
You are faced with some challenges here, no doubt about that. Is the therapy you mention physical or psychological? If the latter, what does your therapist say about the codependency issues you raise here?