I remember that when I started school (in the early 90's), I was also a pretty advanced reader and writer and my teachers picked up on it straight away. They not only gave me extra/harder work to do, but when the class was split into groups it was according to their level of achievement so far, so I was in the 'smart' groups and the slower kids were given easier work, stuff that was to everyone's ability and easily coped with.

Just make sure that if the teacher doesn't pick up on it and that there are problems (some kids will act up if they are bored), that you inform her because the last thing the world needs is more kids running around on Ritalin because their teachers won't go to the extra effort of ensuring they're engaged and challenged by the work they're being given.
Good luck!