Congratulations on this new endeavor. Did she actually breed with a male?
How large, deep is the sandbox? Our velied chams took 6 to 8 hours to complete the digging, laying, covering procedure. If she continues to dig, and starts her tunnel, then she should be fine for hours. When she finishes, covers her holes, and goes back onto her branches- you should then mist her down REAL good and then offer her some food. Be very faithful with the calcium supplement schedule, gutloading, and misting for a couple weeks to get her good and strong.
Let us know how it goes!