It sounds like he bit her out of fear....is your daughter's friend okay? If you're going to have guests periodically I would have them offer him a treat but wait for him to approach them first. Some pups just don't like strangers and I think that's okay
but I wouldn't want him to fear strangers. If a stranger has a treat he may begin to associate new people to something "good". If he doesn't do well with that you may want to crate him when you have ppl over....I have to do that with my "stuck up" boy lol