That guy doesn't really have a valid point. Sure she didn't need to label herself to the XBL community as gay, but I can't see the probelm in doing so. He's trying to label her as someone who validates themselves as gay and nothing else, ehich may or or may not be the case. Besides even if she was it's her prerogative and I can't see any harm in doing so as long as she realises what her actions may lead to (e.g. XBL fags insulting her).
Banning her account is not the right way to go about it, even if it is within Microsofts "rights" to do so.