Relationship

I've been with my girlfriend for five months. She's traumatized by her abusive and emotionally distant mother, and her father left her mom, which affects our relationship.
When we argue, she ignores me, doesn’t talk or discuss things, and never suggests ways to make things work. Sometimes she responds with a sad tone and a sad face, as if she doesn’t agree with me but still agrees anyway, which makes me feel unresolved. She lets me talk for hours without responding. I noticed this since we first started dating and thought I could change her, so I tried to influence her behavior, emotions, and understanding.
I believed she was slowly changing until we recently argued again, and I realized nothing had changed. She still let me talk alone for hours. When I asked her some questions, she answered briefly and told me I could leave if I wasn't happy, even though she had previously said she would fight for the relationship.
When I asked why, she only said, "Fine, don't leave. Please stay," without any explanation, and then asked if we were done.
What should I do?