Agree with GF2, in that you should not choose based on perceived scarcity- our school currently has a glut of bassoons and oboes, and a healthy horn population; they seem to be trendy at the moment. Much better to choose an instrument that speaks to you (your DD) and excel at it because you love it.
Can she try out/listen to some various instruments? If your school has a music program that is often how they start. You can also usually do this in a good music store or rental place, and many symphonies offer "instrument petting zoos" where she could get a feel for different things.
As an aside, one thing to consider is what type of music she is interested in. Things like flute, clarinet, and trombone are all nice because they can play in moats types of ensemble, from chamber to jazz to marching, etc.
Another thought is that at 8, she may not be big enough (hand size is important for bassoon, for example, general size and arm length for trombone) to play anything she chooses.
