At her age it's doubtful she's going to be strong enough or fast enough to effectively use a knife. Besides, a knife is a last-ditch weapon that works best when it's a surprise.

To address what a few others have said... DUELING with knives takes a lot of skill and practice. KILLING somebody with a knife is not the same thing, and to be effective simply requires surprise and a decent knowledge of human anatomy. You ever see a video of a prison shanking? Those guys are never skilled knifers, but that's how it works most often in real life.

She'd be much better off with a 9mm or .38 special and some range time, a good holster and carry style that's easy for her to use (i.e. easy to draw, reliably, every time) and an introductory practical pistol course of some sort.

Carrying a weapon regularly is a way of life, not just a decision. It requires an entirely new set of skills, new mindset, and practice in order to be effective.

The first and most important skill she needs to develop is "situational awareness." See them coming before they get to her. If you can see trouble coming, BEFORE it gets to you, you have a much greater chance of surviving it. This means, sit with your back to the wall, and keep an eye on everybody. Watch their body language. Pay attention to who's doing what.

If she wants to make this leap, more power to her! As an angry, gun-toting, meat eater, I welcome her!