Is she lying about being in a car crash to make me feel guilty?

I think you would be doing something positive for you and her by letting go. It seems obvious that she is using you. She probably does care about you but the way she treats you has to be unbearable. I have heard so many times that if you really love someone that you should be willing to let them go. Your relationship is unhealthy for both of you. If she really cares, she will eventually understand if you choose to say goodbye. I haven't been in your exact situation but I had a best friend who was controlling. She used me up and even stole from me. I had to be strong and walk away for my own sanity. I feel like you need to do the same thing. You could be really lonely and you don't have to your life that way. You have to decide if you should move on or else nothing will ever change.