You can always play the "what if" game. Like you said, anything can be used against you... so no matter what you decide to use to arm yourself, with a little practice and technical training you can minimize the risk or accidents like that. I never said you should rock a 50 cal, just something thats got some meat to it that easy to carry and shoot.
Maybe what you need to do it go to a local range that offers rental guns and you and your lady try out all the different weapons that youre interested in. A lot of fields have rental guns and most have on-site gun safety courses you can go through. Once you see what your options are you can better judge what you think will fit your needs.