13 yr old experiencing extreme knee pain

[emilymayj02]

Recently, my 13 yr old daughter has been complaining of a aching pain in her knee. She is a dancer and has been since she was 5. She has pain in her left knee and has never experienced an injury before except a sprained ankle  (her right). She has been complaining of swelling/hot ache in her knee after dance, aches around them and the other night she showed me her knee after her shower and it was shadowed/black. She told me it wasn't painful but I think that was a lie as she was wincing as I touched it.