Badminton racquets like bike saddles are a very personal thing. Best advice is to go to a local badminton centre that has as shop and try a few out. Depending on her style of play - attack, defence, singles, doubles, mixed - may influence her choice. There are also different handle thickness's. As above, the Karakal PU grips are brilliant and worth getting a couple. Also, the type of string and tension can make a big difference to feel.
My tuppence worth (ex-Scottish U21 player)