... .when I see her and she is completely normal I sometimes get pulled back into the rabbit-hole.
No, she is not completely normal. She
appears so. There is a huge difference.
She seems more normal because you are no longer close to her. She is able to maintain her image of seeming normalcy. However, if you got into a close relationship with her again, she would feel compelled to drop her public face and you'd see yet again her private face.
BPD is a disorder more evident the closer the relationship. Now that you're apart, what you're seeing is her public persona.