easiest thing to do is to record her to see if she is making a fuss and that way you have proof that she isn't to back your claim. You could also ask other neighbours if they could keep an ear out for you, its a little difficult asking neighbours sometimes because noise carries and more often than not a dog you think is next door could quite easily be two streets over.
Second thing to do is to get in touch with the dog warden and ask their advice, explain the situation ie your older dog, reassure them that they are making excessive noise and reiterate the problems that you have had with the neighbour and his dog poos. I found our local dog warden was very sympathetic and gave some very sound advice.
If he has two dogs himself doesn't he hear his own barking?
