Rabbit's teeth can also be trimmed, much like toenails, using brand new very sharp wire cutters or with a very expensive pair of fancy toenail cutters. However this is not to be done by an inexperienced person. I think before anything else is contemplated your friend needs top take her bunny to a rabbit vet and get his opinion....it could be that what looks too long to you is fine or that there really is a problem. This is nothing to play around with....get a definite answer one way or the other.
As Karen points out if the teeth really are too long the bun has difficulty eating which could lead to having the gut slow down, or heaven forbid, stop completely which will kill the rabbit quickly.

Urge your friend to go get a definite answer by a bunny knowledgeable vet and go from there, you may save the bunny's life by doing so.