What do you do to someone who got you fired?

I have this old lady at my work that keeps ratting me out to the boss about stupid things. I currently got into a car accident and i work 6 days a week and i go to school. I only have time to take my car and go to the hospital in the morning for like 2 hours. She tells the boss I always leave work early to do ';personal'; things and she would tell the boss I'm not doing work blah blah when everyone else is slacking off as well. This has been going on for like 5 months. I tried to ignore her, I tried to be her friend again but I just couldn't take it anymore. So I wrote her an email telling her I would appreciated if she just leaves me alone. And she shows the email to the boss and tells him she wants to quit because she's hurt. Now..my boss wants to fire me because of her. What should I do? I hate her so much..what is there to do