I skipped the CHE idea and put the tub on my front porch where it's much warmer she didn't dig anymore nests or lay eggs. I weighed her before I put her in there and weighed her when I took her out, no difference so I know I didn't miss anything. I returned her to the pond last night and am going to try again this weekend with a bigger tub and I'll try adding more dirt and sand. This is her first time laying so I suspect she doesn't really know what she's doing fully yet lol. Thanks for the advice!I don't think you have enough dirt in there, deep enough. If they hit the bottom, they won't lay there. Turtles can be very picky where to lay. I have at least 15 inches of dirt and sand. Also the dirt should be just wet enough so it doesn't cave back in when she is digging. I have some sand mixed in with mine. The che will help also. When turtles are looking to lay they bob their heads up and down on the ground looking for the right spot. They are looking for humidity and warmth for their eggs. I think you are getting there. Just tweak it a little more. If this is her first time, she may dig a few holes before she actually lays them.
You can check for eggs in her by probing your fingers right in front of her rear legs. You will feel bumps. Be very careful though so you don't rupture them. You will know when she actually laid them when you don't feel bumps anymore when you feel in front of her rear legs. Hope this helps. It's great fun to have your own turtle lay eggs!