I hear more and more about cutting ties with people that are a toxic, negative force in your life. Letting them go. How can I do that when that person is my own mother?

I'm always on my guard from her "should have, could have, would have" and I'm overloaded as it is with those. Then when I told her I wanted to start seeking help for my depression, she was so adamant that I needed drugs and rejected the contacts I found that could not prescribe me any. This being after I desperately confessed to needing any help, as long as it was immediate and then after I confided that I was scared to go on meds ( since the last time I was on medication it didn't help). When I found someone, she was overly critical because they couldn't prescribe drugs; I was hopeful/optimistic.

I want to be able to trust her, to come talk to her like she wants me to but things that I've said in the past, in confidence has been flung at me and loosely shared over the phone. So she's lost my trust.

And when I share with her my passion (writing- "oh, I can't describe what it means to me"), she coldly dismisses it. It's not worth anything. It can't bring me financial stability. That's when I go on the defensive which is pointless because she doesn't listen. Then I feel stupid, naive, childish, and my passion becomes worthless.
I don't even want to tell her anything good about me because she'll be too absorbed with watching television or she'll find some negative to point out and I end up feeling hopeless.

Then mom gets mad (and nosy) when I talk to my dad. (I feel like I'm a ping-pong ball between them.)