if she is against killing somebody get a bond arms 45/410. You can get rubber buckshot for them and it will get you away for them fast.
Check local laws and regulations before going this route. This can get one in a heap of trouble should they actually use it in many jurisdictions. If one fires a such-loaded weapon, it still constitutes discharging a deadly weapon, since it is still indeed a firearm. Discharging a deadly weapon at another person when one is not necessarily in fear of "imminent death or serious bodily injury" is a crime. It may be argued that, if the shooter was indeed in such fear, then they should be countering with a weapon so loaded as to be able to stop the threat, and the lack of such a load might mean that such fear didn't exist.
I know, OC and Tasers can be used against deadly-force threats without being lethal themselves, but their use (in most jurisdictions) isn't restricted to
only "deadly-force" threats. The use of a firearm, regardless of how its loaded (even with blanks!) is.
Just make sure that, if she (or anyone else) goes this route, that they still deploy the weapon
only in the same scenarios in which it would be deployed were it loaded with normal, lethal ammunition.
I'd really stay away from firearms if all I wanted was a "less-lethal" (formerly known as "non-lethal") self-defense option. I would also prefer OC to a Taser. In fact, I really should start carrying it again along with my sidearm.
Because stilletto-raggio didn't mention the shortcomings of OC spray, I'll point them out. OC has a limited effective range of five-to-fifteen feet, depending on the size of the container and its stream mass. It's actually not as much a "spray" as it is a "stream", so it does need to be precisely aimed and focused into the eyes. An assailant wearing glasses (sunglasses on attackers is quite common) will have some protection from OC. Wind direction is important as well; one does not want to OC-spray herself if a brisk wind is in her face, but it's still powerful enough that, at self-defense distance, the assailant would likely take some as well.
Advantages of OC over a Taser include the fact that it can be deployed multiple times, is much less expensive to acquire and train with, and that its effects last longer than those of a Taser (up to 20 minutes or more in direct-hit cases.)
OP, don't push your sister into a firearm if she's not ready, and don't try to scare her as well. Commend her for stepping up and accepting responsibility for her own safety, and let her develop that sense and responsibility from there.