I would not dirt from my backyard. I would use about 10widex10deep inches of soil. And I would put it inside her enclosure behind some plants where she will feel secure. I would also get a scrap plant and put it planted in the play sand as they like to lay their eggs beside the roots and it adds extra privacy.
I do agree, if she has a lot of eggs inside her she may be having a hard time breathing and will open her mouth. If she has an RI she will open her mouth. If she is too hot she will open her mouth. But if you say her hottest spot is 80 then I do not think she is too hot. Does she have stringy saliva in her mouth?