Re: Keeping cat out of neighbor's garden
Keeping her inside is the only thing that will stop it. Your neighbor could set up a hose with a sprinkler and turn on the water everytime they see your cat in their garden. This might be enough aversion therapy to make your cat stay away, or it may only work when one can turn on the hose.
You could also create a little garden-like potty-place on your own property and encourage your cat to 'go' there. Rake the solid waste out of it once a week or so. She is using the neighbor's garden probably because the soil is loose and easy for digging/burying waste.