The XBOX wound moulding is finicky, so the only thing we can suggest is to continue to be patient. Make sure you are trying to take the mould of the lower more centered wound on her body.
Nick should also have suggested that you take a mould of the wound- if you forgot a step somewhere [evidence], the game will not let you.
This thread might be helpful:
http://www.csigame.net/forums/showthread.php?t=810