Speak to your neighbor and ask her nicely to keep her pets in her own yard.

Good luck asking her to keep them home...if it works, please come ask my neighbors to keep their dogs home- they poop in the yard, drag stuff out of its place in the barn, bit my dog and myself....
Anyway- there is a product that you put in the soil- I'm sure someone here will know the name- it is supposed to repel dogs and cats also, I think. I'd hate to use mothballs, as they stink to us and I do not know if mothballs really work. Can you temporarily put rocks/shells- something like that so the cat can't dig in the dirt to 'cover-up'? If it can't 'cover', it might not want to use it as a litterbox??? Spray the cat with a waterhose if you are able to...might make it think twice..

I have cats and house-plants,best way to discourage them is putting a piece of screen to fit the pot - a hole cut out for the plant, and then cover it with decorative rocks.
Another method would be to place a lot of little sticks in the soil, they are not comfortable to walk on.

Sprinkle the top of the soil with cayenne pepper. No more problems. It will disappear with the rain, but the cat will have already learned its lesson.

It do not think it is realistic to expect a neighbor to prevent their cat from going on your property. They are not like dogs, which you can insist stay off your property. But cats a universally known to roam all over at will.

I've also heard cayenne peppers works well. You could also keep a plant of catnip on the other side of the yard...they will pick that over the other plants anyday!

The only reason cats roam "at will" is because of irresponsible owners who let them.
Cats should be confined to the house or in a secure area in the yard, just like dogs.

Weed I agree with you but I was not going to mention it :-) If its a pet it should be treated like any other pet and not left to roam and annoy others. I could not imagine just letting my dog roam around my neighborhood and I'll never understand why some people with cats think its okay to let their pet cats trespass.

If you see the cat at your plants, turn your hose on and give him a little spray. It will not hurt him and maybe his owners will get the drift when he comes home wet.

A combination of tactics will probably be most helpful. Screen placement over the top, using pine cones (or sweetgum balls) or other, a mild vinegar and water spray if you catch the cat in the midst of it. I'd not recommend the cayenne, which could cause problems for the cat.

As far as asking that the cat be kept out of your yard.....good luck! BUT, you could (in a friendly manner) ask them how they keep their cat out of their own plants! Maybe they'll take the hint and start keeping it inside. At the very least, they might have some good suggestions.