So sorry to hear the pigs have been attacked again. I don't think you reported the other attacks to the police? Report the owner now, mentioning the other attacks. The police will warn her to keep the dog under control - next time it will have to be PTS. Castrated or not, this does not make a difference once a dog starts to attack livestock.
Your pigs have a right to be safe in their own pen - you have given the owner enough chances to contain her dog. Surely she must realise there is no way this dog can be out in a garden unsupervised even for a minute? She is responsible for the dogs actions. I would also give her all the bills from the vet, and ask that she reimuburse you, its the least she can do.
I have dogs myself, two of which ended up getting shot for going among a farmers sheep. They had been with me 8 years amongst our livestock and never bothered. I told the farmer had he not shot them, they would have been PTS by my vet. Once a dog starts to attack livestock, no matter how much I cared for it, thats it.
If this dog is not stopped now, and does it again - what if you are not there to stop it? It could kill the pigs. I am afraid that the feelings of the neighbour, or indeed the dog, have to take second place to the welfare of your livestock.
I do hope things can be sorted to keep your pigs safe.