Sorry to hear about your friends accident... I ride a Ninja 250 as well and in my opinion the rear brake is great for slowing to a rolling stop at a stop sign. beyond light braking, the rear simply does not cut it as the rear becomes so unweighted that locking the rear is annoyingly easy. unless I happen to be riding on gravel or a situation with poor traction, I always have two fingers covering the front lever.

Like you, I am a firm believer in front brakes. That being said, your friend made two mistakes: first and obviously she used the wrong brake lever. Secondly, if your friend had correct braking posture and technique she would have hit the car directly in front of her. (I am very glad she didn't) Because your friends rear end slid out, she must have been leaning to one side or must have put unequal pressure on the handle bars. Good braking posture dictates staying completely vertical and putting little pressure on the bars to get the most breaking force out of your rubber

What I'm saying is, go out and practice your stoppies!!! Put all your gear on and get there gradually!