Is it rude that my grandma sent me a present she rewrapped from Christmas?

I agree. It WAS an innocent act on her part. Since you're her grandchild, she probably thought that you would be more open-minded about it (she definitely wouldn't act like you didn't know that it was given to her). Christmas tree ornaments given by family is more important than you might think... she's your grandmother! Family is family. Don't take these things personally.