Oh its a hard one eh..esp if they are good neighbours..
But i wouldnt like if my boy got bitten i would just to talk to them to get it resovled as it could get worse as it has bitten 2 of your kids.., i would put something around fence to stop my kids hands/finger to go threw the fence and i wouldnt let my kids in there garden until i knew it was 100% safe..she is a mother to she will under stand..