My (21M) girlfriend (20F) is an extreme people pleaser, how can I help her?

Throwaway account. Me and my girlfriend have been dating for almost a year now. I always adored and admired her because she was really out going and likable while I'm way more reserved. Because of this, I could never predict her people pleasing tendencies.

So about a week ago while we were having sex, forgive me if this is too kinky, I choked her and she had to use our safeword which she had never used before. I was quick to stop and comfort her and ask if she wanted to talk about anything. She said no and that she could still help me get off and I declined because I was super uncomfortable. I had just pushed her to the point of having to use our safeword.

I made her talk to me about things she liked and disliked about our sex and she asked me what I disliked. I told her she's overenthusiastic, she always immediately says yes no matter the situation. Obviously consent is sexy, but seriously there's never hesitation she always always gives in. She then dropped the bomb on me that she's unable to say no to me.

I told her that that was fucked up, because now I'm unsure about the times we've had sex and she was actually into it. She tried to justify it by saying that she wouldn't want me to deny her, so she didn't want to deny me. I tried telling her the importance of boundaries but she kept saying she doesn't have very many when it comes to me and that she'd do anything for me. She started sounding extremely codependent, especially when I told her she should find help and she just said the only person she needs is me.

I walked out on her because I was unable to find a middle ground, and honestly it scared me how anxious she was acting. She kept saying that I hated her and that I think she's fucked up. Whenever I tried to bring up things from the past she'd tell me to "stop it" which I find destructive since she can't accept the truth. I don't want to keep having sex with somebody who lies about being in the mood constantly. How can I help her set up boundaries and learn to say no?

TLDR: My girlfriend admitted to me that she's unable to say no to me sexually because if she's able to please me she wants to. I tried to convince her it's not healthy but she's to stubborn to understand the depravity of it all. How can I help her see?