If it weren't for the mystery item that was with the clothing as well.
My guess is the clothing has blood/evidence hence the reason that and the mystery item needed to be disposed of. Otherwise it would make more sense to state what she is actually wearing or to make up an outfit. Making up an outfit that never existed wouldn't require the extra effort of then having to dispose of it.
But criminals often aren't masterminds either so I suppose grabbing a clean, unworn outfit and disposing of it then claiming that's what she was wearing instead of what she was actually wearing is possible, but what would be the reason for that?