Red ear sliders usually lay between 2-4 clutches of eggs, since your turtle laid two clutches, and you can still feel eggs, it is very probable it has more to lay, a simple x-ray will reveal whether it still has some eggs to lay. Sometimes turtles stop digging and do not lay their eggs because they feel something is wrong with the current nesting site, they then move on to different sites and dig until they the nest feels good enough. Your turtle may not be satisfied with any of the nests and so has been rescheduling her egg laying. Turtles will stop digging if they feel there are too many obstacles in their way, which may be possible in your garden. You may want to try making your own nesting area for the turtle, then you can control the conditions in order to ease the digging and make it feel like a good nesting area for your turtle.
Since your turtle has somewhat settled down, it may have laid the eggs without your knowledge, reportedly, some turtles are aware that the eggs are infertile and so they may just drop them anywhere, including in water.
Another possible reason is, of course, the eggs have binded. Turtles may show signs of egg binding, there may be swelling at the cloaca, your turtle may become depressed, and as is currently happening, she may dig but not lay her eggs. If this continues then you do want to consult a vet, since the eggs can calcify and rot, and cause bacterial build up and eventually disease(and maybe kill) your turtle. If your res is still frantic and continues digging but fails to lay eggs, then it's quite likely the eggs are bound. Eggs can bind for a bevy of reasons: stress, wrong diet, eggs are too large.. If so then they may have to be removed surgically, and of course, a vet is needed for that.
Keep in mind clutches aren't identical, a turtle might experience a difficulty laying a particular clutch it didn't experience with other clutches.
Feel for eggs in your turtle, they may as well be gone, since it seems it might have settled. If they're still there then offer a nesting site you made, or if you can't place it in the garden. If failure during laying continues, then it's recommended you consult a vet to remove them surgically or to give your turtle oxytocin in order to induce laying the eggs. Though many people simply give their turtle time to lay them and eventually the turtle do manage, their is still a definite risk that ought not be undertaken.
Great job rescuing your turtle, below I'll list a few sites you may find helpful: