Your friend sounds like an emotional vampire to me; putting you down to make herself feel better. She knows you are empathetic and will feed her ego with your genuinely caring nature. She knows she can take advantage of you and use gaslighting and other manipulative psychological tools to keep you on the hook. Keep standing your ground when she tries to interrupt you in order to one-up you. It will feel scary to be assertive, until you become comfortable sticking up for yourself. Good for you.