Slash all the way. My local track runs them and in 4 months of racing them i've seem 3 break(all because of hitting an I beam going down the straight). I raced a rustler last season in the stock class with 6 cells and I would not break. I ran it into walls and I ran into I beams and the thing would just keep on going.

Slash would be perfect since it is about the same size as a 1/8 buggy...she won't feel like she driving a smallish truck while you guys are running your 1/8 scales. Tough, inexpensive. She's going to run whatever she is driving into the curbs so might as well get something that stands a good chance at surviving the hit, and if it does break something parts are inexpensive and plentiful

Just install a proximity sensor on all corners of the vehicle and then feed that to a throttle override unit....

Summit.
 

Buy her a Summit and put her into crawling mode for a while. She will probably enjoy that once she gets started with it. At least you can keep her from driving 100mph all over the place.