In my limited experience, the mental health diagnosis gave the person free license to justify all her horrible behavior and not have to apologize or feel bad about it.
Sorry you are going through this. The above statement sums up everything you need to know - she says needs a caretaker and she knows you want a relationship. She will offer the relationship in order to get the caretaker.
You will get nothing.
xizor is correct; her knowledge that she has a diagnosis is generally a free pass for narcissists - they do what they want without a hint of guilt or self perception. They will crush anyone for the slightest amusement.
For your own safety you should say goodbye and walk away, nothing good will come from this. The lie of a potential relationship is just the last event in a game of torturing you, the last chance to crush you. You know better; don’t do it.