Neighbor's dog

I need some advice. We live in duplex and our neighbor on the other side of the wall is "dog-sitting." I say "dog-sitting" because this is what she says she's doing, but the dog has been here for about a month. I really wouldn't care, except the dog howls and cries when she's gone... and she's not home very much. I'm in the second year of a masters program and trying to do my research and projects with a dog howling and crying for hours just isn't working. In addition, the dog howls through the night making it difficult to sleep. I've told her about the problem and our landlord has told her that the dog is not allowed to be there. I know the next time I mention it to our landlord the dog will be out of there, and the thought of this poor dog becoming homeless because her owner is irresponsible breaks my heart. However, she was never to have a dog in the first place and at some point in time the landlord will find out the dog is still there whether I tell him or not. Any suggestions on what to do?