If it's a female and she's of age, she's looking for a spot to dig and lay her eggs in some dirt. Get a 10" deep bucket of moist soil/sand.
If not, check your temps. Could be too hot/cold and looking for warmth or shade, although your enclosure looks good in this regard. It could use more solid basking branches though. Place some horizontally at a few different heights for basking options and temperature regulation.
Do you free range? Maybe she just wants out!