Recommendations will come in from near and far, as far as the requirements you list. Making it simple, I find it interesting that from what I understand, your historic "hitman" used a 22 and used it fairly close up. I do not believe your sister will be getting into any kind of gunfire exchange at distances greater than lets say 10-20 ft max, period/end of story. If it is good enough for a professional killer, it should be lethal enough for self defense. 22s are relatively inexpensive and have the very lo recoil you mentioned more than once. They can be small in size, which may suit your sister, easily carried, and low in weight--the cartridges are also small and light. Replies will be forthcoming that, perhaps, make fun of my choice and offer up the calibers above the 22---they can be inexpensive, particularly 32s and 380s, but they are not lo recoil. Once you get above the 380, your two-time comment on recoil becomes an irrelevant standard. Higher calibers should still be considered--just because someone is a woman is no reason that proper training with higher calibers would still be a problem due to recoil. Many of the best "shooters" around are women--they seem to have an innate sense of self that with training ends up making them more capable and accurate than men. Another possible choice is not a firearm--good, really good sprays and electronics like tasers etal will provide that immediate self defense that may be as good as the 22 although the 22 can be lethal and final unlike these other choices. Read the comments, google for more comments, go to gun shows, go to a good gun shop. Hands on advice and handling of devices is a needed prerequisite.
