Train Your Dog to Stop Digging
Your dog may be digging for any number of reasons - the main one being that it is "working" for her. In other words, she is getting something she needs or wants out of the digging. Perhaps she is trying to escape, entertain herself, get rid of excess energy, find a lost bone, get cool by making a hole to lay in, catch critters, visit China.. who knows! Enough speculation, let's solve the problem!
First, make sure that she is not allowed in the yard unsupervised. I know this can be difficult if you have become accustomed to giving your dog lots of free time in the yard, but a habit cannot be overcome if it is allowed to continue.
Go out in the yard with her. If you see her digging calmly say "enough" or whatever comes naturally to you. If she stops, say "thank you". If she continues, say "time out", go and get her (hint: have her drag a piece of rope if she is difficult to catch), bring her in the house and be really boring for a few minutes.
When you do a Time Out, it is best to be very calm so that you don't accidentally teach her that you are scary.
It is also important to set her up for success by making sure that when she is outside she has something really important to do, like hunting for her breakfast. Scatter her kibble all over the yard or fill treat toys for her. Maybe a fresh/frozen marrow bone would do the trick.
You might also consider creating a legal "digging zone" by setting aside part of your yard and burying some treats and encouraging her to find them. You could also make a digging zone using a kiddie pool and play sand. When she digs in the "wrong" area, she will get a calm Time Out, and if she digs in the "right" area she will get treats and praise.