there are a few options. the simplest is just stop paying and stop going to class and take chances on whether he/they will sue or not. ...thats a bit risky since it could drag on and may ultimately affect credit reports. and she may end up being court ordered to pay anyway.
tell her to check local laws and find out her rights. then check for similar cases and outcome. It helps if your friend happens to be a student still living at home or a minor.
get a decent lawyer. when he/they get a letter from a lawyer, he/they will be more willing to negotiate reasonably out of court.
as cxt asks...what state is she in and how old?
also see: http://www.24fightingchickens.com/2006/09/29/contracts/http://ntfa-dallas.home.att.net/mcdojo.htm
not sure if this would work...but read the contract over again and look for things like this:
there's often a clause that if you physically become "unable to participate any longer", or it's "detrimental to your health", they'll let you out of it. I've "heard" of some people spending $30 to go see their doctor, telling the doctor their knees hurt all-the-time and they think its due-to-kicking in karate. Then asking their doctor if he'll write a note saying "I recommend you discontinue karate immediately for the sake of your knees" so you can get out of the contract. I've "heard" people have easily and successfully done that and were released from their contract!!!
or you could go the 'mislabled self-defense' route (which is why mcdojos are now avoiding that particular phrase). It could be argued that you aren't getting the training as advertised.
alternatively, find out if the school will let you transfer your contract to another person wishing to join.
contract law in general:
good luck. don't sign Martial Art contracts.