Hmm, well I'm not sure I'd be happy to eat salad type veggies if the cat constantly uses where they grow as a litter tray, specially if the animal isn't wormed frequently. If it was veggies which were going to be cooked, fine. Can't you stop the cat from using the area? Cultivate somewhere else in the garden - its only because the soil is well worked and nice and loose that the cat goes there.

I don't blame her. Get some cheap plastic stretchy netting and cover the area - its the stuff used for runner beans or peas etc. This should deter cats.

Also depends if the cat used a neat hole and covers it or if it sprays. I wouldn't worry about the first overmuch but would avoid the second!