How long is the dog being left? Is it for an acceptable amount of time? Of course some dogs hate being left whether it's for 10 minutes or several hours. There was a programme on TV a little while ago on this, where they put in cameras when the owners went out and a lot of the owners were very distressed when they saw how upset their dogs got (some already knew about the barking from their neighbours!). For the a lot of them the situation was improved through the right training, without that I would have thought the dog is unlikely to "get used" to being left on its own because it's going to think "I bark and eventually if I bark long enough my person will come back". I would say your neighbour needs to seek the advice of a trainer but how you get her to do this might be another issue! Good luck - I own a dog and love them but a couple of times have been woken up by some poor dog frantically barking - it's incredibly irritating as well as being unfair on the dog..