she will stop if you train her to stop... but ONLY if she is getting adequate amounts of exercise.. Border collies are the smartest breed of dog, and as such, they require stimulation, mentally and physically.
If you run this dog, or walk with this dog, or even throw a ball around to her for at least an hour a day, preferable 2 hours... she will drain herself of that negative energy and be much more inclined to stay in the yard... digging is a sign of boredom.
With an autistic child however, I feel like you may have your hands and schedule pretty full, so if you cannot make time to exercise the dog, perhaps it may be time to give her away or get a different, lower energy breed... like a bulldog or basset hound.
To train, put her on leash, let her wander the yard and begin to dig (if she will), give her a tug, quick yank back as she is digging, and say firmly, no. when she stops, do not immediately give her love and support, or she will think of it as you loving her for digging. be firm, each time she goes back, you tug and say NO in a firm assertive voice... soon try it off leash, and give her corrections as needed.... when she stops and turns to leave the area.. give her a treat to reinforce her good behaviors