You've got the right idea with trying to make the area unappealing, but unfortunately a spray isn't going to do much (the digging may in fact be at least partially in response to the spray, in an effort to get rid of the scent from it).
I'd suggest a two-pronged approach. The first is to deter the cat from the area in general with an automatic cat repellant that will go off whether or not you're present. Options here include "Ssscat" motion-activated air cans, and "scat mats," flat mats that carry a mild charge. Neither will hurt the cat, but both will startle her when she approaches the plant. For a lower investment, you can start with trying a sheet of aluminum foil on the table or shelf under the plant. Most cats don't care for the way foil feels under their feet, and will avoid the area. If you do this, I strongly recommend using some blue painter's tape to secure the edges, or she may tear it up trying to get rid of it.
The second prong is actual prongs. After you've made the area in general unappealing, make the dirt itself unappealing. I've used toothpicks in the past to stop a cat from sitting in a pot, but anything that sticks out of the soil and is spiked will make the area unappealing; you might try plastic forks planted tines-up or other items. Don't use anything so sharp it can actually cause harm (needles/pins, knives); you're just discouraging the cat, not hurting her. Err on the side of "too many" rather than "too few," and be prepared to put them back a few times before she gets the idea that she can't get rid of them.
Give this approach a few days, and see how it works out; if after a few days, she's still getting past all your defenses, you may need to find a way to put the plants out of reach, but as long as she's not eating the plant and it's not toxic to her, toughing it out for a few days should hopefully get you to a point where you can keep the plants where they are.
