Very sorry to read this story. It's shocking to experience that, and is most unfortunate. I carry everywhere I go except where not allowed. A gun or other weapon is a choice of last resort; your primary weapons are your head, eyes, and ears. Essential to stay ahead of the situation versus walking into one.
I've used a handgun twice in what I believe were situations where considerable harm was intended to me. I only had to draw it partially out and that stopped by perpetrators but you really don't want the situation to get to that point. A very wise master shooter once taught me, "Avoid trouble, run away from trouble, stop trouble", in that order.
Hand guns require a lot of practice, super fast access, and at arms length you can still get into a grappling situation which is very bad unless you're a highly capable, strong, and agile person.
Tasers are a good option for less than lethal response but not good for multiple assailants. I'm not a fan of OC spray though I have a fair amount of it in different sized cans; it's too easy to have it blow back on you and that stuff is seriously nasty.
Good luck; advise your friend to take a hand gun defense course for civilians. Many of those are bogus but a few are quite good. A good course is mostly about awareness, and options prior to drawing a weapon.
Good luck; stay safe, most people are good but the bad ones can be very bad.