Look at my other message, too
It is OK to water the garden as you have always done, except do not flood the area with lots of water. Wild turtle nests get rained on, so they are able to withstand some water in the nest cavity-but most time very little gets in. A well made egg chamber has the sides well pressed by the female turtle's heels, and a thin, but harden layer is made. It will stop water, unless there is a flood and the ground becomes saturated.

Since you have had other hatchings, your locale must be somewhat conducive to the eggs. The female picked this spot, so you can feel confident that you gave her the option to making her nest where she wanted.

Now your job is to expand on the pen where the female is held so she won't have the stress of pacing and laying eggs outside the safety of her pen. As you noted, make a big area for nests in the pens, this could be an area of sandy loam with planting of bunching grasses instead of sod.
Tess