A.P.
I was a pre-k teacher in my early twenties, and was invited to many birthday parties and student functions. I didn't think it was weird, and was always very flattered when students chose to do this. I was not able to make it to very many, but I did go to a few, either way I always felt special that they thought of me. I say go ahead and invite, but don't count of her being able to attend, as someone else mentioned, teachers do have have their own lives and can't possibly make it all the things they get invited to, but it will make her day to get the invite. Also, I would hand deliver it and let the teacher know not to feel obligated, and that you understand if she can't make it.