Hi there! You've received a lot of good suggestions. I would ask for the gifted testing, and I agree you should ask immediately. If your child tests as gifted, then you can deal with your options...if you want her in a gifted program in the school, or if you want her challenged in the classroom only by different work, or both, or otherwise. You can have a lot of say in this through the GIEP (Gifted Individual Education Plan).
If, for some reason, your child does not test as gifted, do not fret. You still can make requests for the additional challenges. The important thing is to be well versed in your rights, like one of the posters said.
I love the hoagies and PAGE websites that someone else mentioned. You can get great info on a lot of things, even if your child ends up not "making the cut off." Pennsylvania recently changed the laws and it is a bit easier to test into the gifted program now, but being in the gifted program is not the be all and end all. Getting appropriate work for your kids is!
The Hoagies website is http://www.hoagiesgifted.org/ . The PAGE website is http://www.penngifted.org/ . Even if your child does not test into the program, these sites can help you.
Also, does your school ask for letters regarding placement? We are not allowed to make specific teacher requests, but we can write a letter regarding our child's learning styles and the like, for those making the placement decisions to consider. I always take advantage of this and ask for the teacher who will keep my child extremely challenged and motivated, etc.
Also, if your child is placed in the gifted program, the advocacy does not end there! The GIEP really needs to be INDIVIDUAL, but often they are pretty generic, so you need to advocate for that.