Hi there. In my experiences even a young leo that produces infertile eggs can lay them quite normally. I think that as long as she is getting plenty of calcium she will be fine. You can dust mealies by placing them into a food dish and just sprinkle on some of the calcium dust once or twice a week. You can also use the lid from a pop bottle or any small dish and just put some calcium into that, the gecko will eat it when she needs to right out of the dish

I think you have done good not giving her crickets because you use sand. In my opinion sand is not safe, but so many people use it (even some breeders) that I suppose if you take precautions it's not always the worst thing. Also, you can very easily tell if she is gravid by looking at her belly through something clear. I like to place them in a deli cup to check. The ovals will be about nickle sized, one on each side. Good luck with her, I think she'll be fine, just get that calcium into her
Julie