This could be a really tough one without seeing the situation. I don't think this a "new" behaviour but something the dog is re-discovering. The fact that he could be the boss with your daughter when she came to let him out - remember the dog is trying to do his job when the real boss (you) is away by protecting the territory - and got rid of the intruder has reinforced it. It is the whole postman/van (mailman) thing really - some dogs go nuts when the post arrives simply because when they bark and growl the postman goes away (it doesn't matter to the dog that the postman will go away whether they bark or not) so it is a rewarding behaviour as what the dog wants to achieve actually happens and the dogs feels that it has protected it's territory well.
It will take a great neighbour or a fab daughter to overcome this - not fair on a daughter who has made her feelings clear already, I feel! If the neighbour is willing, however, then progress can be made. Start with the neighbour calling to let the dog out when you are in the house, the neighbour could take the dog out and go through simple excersises like "sit", walking to heel, "stay" and come. This will establish some respect and status. Then try it with you out of the house but close by so if things go wrong you can simply walk by, say "Hi" to the neighbour and ignore the dog - then he will know where you think the pack structure lies.
If your neighbour isn't up for that then you may have to look further afield for someone to do this for you.