Suggestion - if the girlfriend is being 'weird', tell her that the law will only give a blood relative POA - not your fault or hers. She is afraid of being excluded, maybe, so if there is a way of telling her how she can help where no one else can - such as, she is right there and knows how he is behaving, and can give a first-hand report that no one else can.

Not wording it great, but you know what I mean...I hope....

HUGS!