The food is similar too, although I use a lot of carrots, because she seems to eat them more than the other foods I've tried (mainly apples and cucumbers). Because it's so similar, there is no obvious reason why she should have felt comfortable enough to lay eggs... My hypothesis is that I put the enclosure in the sun for a couple of hours every other day, to give the plants sunlight. It makes the sand get pretty hot, but since she is a desert beetle I figured she could take it. Maybe the heat helped convince her to lay eggs, or at least helped the eggs hatch into larvae.
So, she will be in the bug guy's care for a week, and he is hoping to see the egg laying behaviour we observed, as well as find out if and what the larvae are feeding on... Of course now I am super nervous about getting the larvae to pupate!