Please don't take this the wrong way, because believe me, I have been there - but why is it important for you that the teacher knows she is gifted? Is there something (in terms of accommodation) that you would like for your child? It might be easier to say something like dd3 really likes to put together puzzles with lots of pieces - would it be OK if I donated a few to the classroom?
As the mother of three children who read before three, it has been my experience that having them read at that age will not necessarily translate into the teacher "getting it". I've been down that road with my first one. My middle daughter (now three) can read and it was clear from her "report card" that the teacher has absolutely no idea. The report card noted, "dd3 now knows all her letters!" (uh yah, thanks for joining us a few years late.) I am debating as to whether or not it is necessary to even mention the fact that she can read to the teacher. Sorry - I think I am just a bit jaded from my first.
As far as the hot-housing - I don't see anything wrong with supporting your child to do their best work. Being challenged and accomplishing things (whether it is mastering reading or putting on your jacket) are an important source of self esteem. There is a fine line between pushing and supporting - but it seems like you are being pretty reflective about that.
