she definetly sounds like an idot.
I too have public walking past one of my fields, the way I see it, the world is full a idiots and its my job to protect my animals so I ripped out all the fencing and installed 5ft high tornedo fencing, nothing can get into my fields, I can sleep at night.
The law says "a dog must be kept under control by its owner at all times when on a lesh or not. Worrying livestock is an offense (shee, goats and horses are stated as livestock) but killing a cat sadly is not (

{ ) and if they kill another dog it is a rap on the knuckles, I know this from bitter experience as my mothers small dog was killed last year, I lost my will to fight over it as my mum sadly died not long after, a gutting time.