It's very possible she is gravid. Build her a nesting box a la Deer Fern Farms:
Also, you need to make sure your rocks are on the ground. If you are worried about them scratching the glass, put a towel underneath them and then cover it with sand. Uros will dig underneath the rocks and can kill themselves.
Make sure you keep an eye on your pair as the female could become aggressive if she needs to lay. Good luck.