“I believe my sister should carry a stun gun “
Why wouldn’t you advise her to defend herself using the most lethal weapon possible (legally, of course)? There are plenty of compact firearms and confidence comes to a woman who can defend herself. The magnitude of the threat should determine the ferocity of the defense.
Yes, I think a nice 380 is better. For most women. Some have aversion to gun.
I think even 9mm is under powered in some circumstances. Depends on how it is loaded.