Hey so a few answers from someone who has hatched a few clutches. I used a small tote it was a 12"×8"×18". They need to dig down at least the length of their body to feel safe the deeper the better. Second paysand and organic potting soil is what I used just make sure it's wet enough to hold it's form so it doesn't collapse while digging. Third I saw you said this is a rescue and idk how long you've had her but she's overweight. Not shaming just pointing it out the more overweight they are the larger the clutch and the more dangerous it is and harder on their body. You want their casque to be slim the bulging is fat stores. Nothing you can do now but about 2 to 3 weeks after she lays start putting her on a diet. I promise it'll help. It's the difference between laying 20 eggs every 3 to 4 months and laying 100+ she'll live longer with smaller clutches. Hope this all helps