Hi,
Well that's actually a tough one. If she has a good brass teacher (not a band director who plays clarinet!!) it may be worth having a chat. In my humble experience, however, if she is a student player and providing she is playing on a reasonably well made mouthpiece she is unlikely to NEED another mp. She may want one because she feels that it's holding her back but IMHO that's very rarely the case.
If she is a reasonably advanced player then the arguments for NEEDing a new mp based on sound and comfort become more compelling. There are as many variables at this level as there are different mouthpieces.
On saying that of course even very good players believe that the next mp they buy will be the 'Holy Grail' and have drawers full of old ones...not me of course!!
