Taking advantage of your condition

birth defect.

oh gosh gibby... I didn't see that thanks

I'm guessing it's more of a quirky thing she can do. She may have low muscle tone In her leg from birth trauma and normally wears a brace. Or she could have tendons/ligaments/muscles that bend and stretch more easily. One of the zombies in Resident Evil, (who was also the choreographer), could dislocate his ankle at will and used it to make his character more freaky.

Or she could have actually been born with a reversed foot...

Looks like a wig I think.

Well yea but I think she could of made it messing and bloody...