I don't have any answers for you but just wanted to say that I am suspecting I have a similar situation brewing here.
DS 2.10 will look at the letter M, but instead of saying it is M, which he easily knows (he has known all his letters since well before 2) he will turn the book around and insist it is a W.
Seems he is always trying to make things more "creative". Like he gets bored with looking at something for what it is. He always jokes around saying the wrong thing and either laughs about it or puts on a straight face.
I hope he grows out of this because I can see it becoming an issue in school later...
I REALLY hope someone has some experience with this and will post suggestions. I DO think you should have her tested. We tested DS4.11 and it had made things so much more clear for us. It is like I know my child so much better and understand his behavior better.