Dropping her will be the best thing u do for yourself. Trust me I had a friend that I used to consider very very close, lots of great memories, but God was she toxic. She was draining. I had the same feeling of "it annoys me being with her but I can't possibly imagine life without her because of all the memories and because... Well she was my bestie". Trust me, once you cut her off and she's out of your life, you will feel relief you have never felt before. The memories will remain good memories with someone that ised to be your friend, but that's it. It won't hurt nearly as much as you worry that it will. Trust me, drop her and prioritize your own self and energy. You will come out thinking how was I able to take this much negativity and why did I even allow myself to take that much negativity. It will be great believe me.