I just want to send my thoughts of support. I don't believe what you are going through is all that uncommon. Yet, I can comprehend how and why you're struggling to draw that line for your own peace of mind. I'm certain beyond a doubt that my own ups and downs affected my own mom similarly. Enough so, I believe, that her widower wasn't too fond of me. They married after my oldest was born. But it's that type of mother daughter dance that's lost on any other third party than the father of the daughter.
I don't really have advice. Just a sense of knowing without knowing as a mother of all sons. The adult mother daughter relationships do tend to evolve into such.