There is a reason Crossfit's detractors will call its devotees "anorexic." It doesn't lend itself to bulkiness unless the practitioner has the genetics for it, and most women don't.
Sufficient calorie restriction, a la Zone, plus tons of metcon and very little strength work and/or heavy weights will strip the muscle away, though it's going to take time. She realizes her lifts are going to go down though, right? I bet an even better method would be some form of long, slow cardio, like lots of running and bike riding.
Hopefully someone with more expertise in this replies--I don't know how one would strip the "bigness" while maintaining strength, or even if it's possible.