My vegetable beds turned into cat litter boxes when they were fallow and it was very frustrating. I don't know how big her beds are or if this would be practical for her but I have used weighted down chicken wire. The cats don't like to step on or "scratch" on the wire. I have seen the odoriferous repellents but have reservations about how well they would work (and they might have a different objectional smell than the one she is protesting now). At least they would need to be reapplied so often due to rain I doubt they would be worth it. My two large barking dogs are available for rent. :) They do a very good job of keeping cats out of our yard now.

bark mulch, gravel or rock mulch is even better. chicken wire, plastic bird netting, heavy planting so there is no bare dirt.

After I prune my roses I scatter the trimmings where the cats go. It works!!

Neighborhood cats come through and poop right on top of thick lush grass. They use the raised bed cottage stones as catwalks.

A super squirter squirt gun aimed well while barking like a dog gets them out of here fast.

There was a LONG thread about this fairly recently, hopefully still able to be drawn up via "Search" ...

"A super squirter squirt gun aimed well while barking like a dog ..."

Now THAT is a visual...lol.

But I must admit I've been know to go running out the door in pursuit of a cat spotted in my yard, yelling & waving my arms. Generally, my purpose has been to keep them away from the birds that enjoy my yard, but I don't want them pooping here either. I've really freaked out a few cats!

I have the most faith in cobbles, these make it impossible to get at the soil and dig in it. Dry flour-like soil seems to be the biggest draw, the less like that a spot is the less appealing it seems likely to be (although I too have seen lawn used). Where the soil is to be kept open, as in a vegetable plot being used for warm season kinds that need to have the sun get in and warm the soil, it seems the only sure remedy would be something like row covers clipped in place so the cats can't bat the walls aside and come in.

A friend living in Shoreline, WA (north of Seattle) has his vegetables under cloches much of the year anyway, for the added warmth and frost protection. But these do come off during hot weather, so cats could get in then.