While I have seen even young hatchlings lay up on their sides it's not something they continually do.
Breeding females will do this quite often during the cooling/building stage.

Bowl wrapping, sitting on top of the water bowls, dipping parts of their body or even their whole bodies in the water and laying inverted are what they do to stay cool while growing follicles.

Just keep pairing the male with her until you see an ovulation, then stop pairing, stop feeding the female and wait for the pre-lay shed then eggies

Good luck!