What do I do about a neighbor who keeps slamming her car door into my car?

Kick a dent into her car. In fact, since it's a hoopty and she probably won't care if the bodywork is dented, kick one of the headlights out. If she does more damage to your car drain the brake fluid and follow her filming her driving the POS car and post it on YouTube when she runs it off a cliff or something. A Mitsubishi Eclipse is too nice a car to be treated this way so if she survives the car crash tell her you paid lots of money for that thing and you worked hard for that money therefore you should be entitled to SOME dignity.