Self defence- period.
You can't use a gun for any other purpose than self defense. You can only use it to protect your own life- not shoot assholes.
Get a .22 auto. Larger guns have more recoil which will, on average*, intimidate a female shooter. Your second shot is just as important as your first. Aim for nipple height at the center of the chest, 2 inches to the right if your good.
*I've found that women are actually better shots than men.