Is my red ear slider male or female?

We thought that it was a female because it has short claws and an closer to the shell than the tip of the tail. It is about 5-6 inches long, but we don't know how old it is. We recently put a blue rock in the cage about the size of a turtle's head. It started doing the courtship ritual (arms out, shaking claws against it) like males would! It seems quite infatuated with the rock, but now I'm wondering is it a male? Or is this just some weird behavior that a female might do also?