I tend to agree with the second psychologist. As someone who has ADHD, I think a puppy would be a good outlet for the child's energy, and it would teach the child responsibility and commitment, as well as giving the child a friend.

Secondly, I don't think there is much you can do, since they already have the dog. I mean you could tell them to get rid of it, or make them leave, but that seems a bit extreme. I think that since whats been done is done, the best thing to do is approach them about not waiting for you to discuss this, and then follow protocol and charge them accordingly (90$ a month or whatever you said above). If they can't pay that, then deal with it as it comes.