I had a similar problem. One of my neighbours children was, along with another child from our street annoying my ds2 constantly, especially at school. I went to the school and complained. next day i was met at school, (while all the children were lined up) by child X's 21 year old mother. Child X was 7, and two years older than my ds. She had a right go at me, asking what gave me the right to go to the school about her child, her child was a wee angel and my son was - and i quote her here-
"A Fking little st who need a fking good kick up the are, and he had better watch himslef". We live in the military community, and she then started on about my DH, and his job and then on about me, calling me all the fing things under the sun. This, as i say, took place in front of all the children,parents and teachers. However, i didn't answer her back, i just stood there and let people see her true colours.
I think what i'm trying to say is, carry on as normal, it is difficult, especially if there is a disput over a bill (been there, done that) and you think she is slagging off your DH. Try not toworry, rise above it and try and carry on as normal. We did with our horrible neighbour, to the point of always shouting "hello" whenever we saw them