They can actually be gravid (Carrying eggs) without a male present as well.
You can very carefully feel for eggs in front of her hind legs. You need to be very gentle though. It's possible to crack an egg by doing that and that would be bad for her.
Usually when gravid, they are desperate to get out of their tank, because they need to lay their eggs on land and bury them. They will do a lot of kickinng and digging with their hind legs.
A quick xray at a vet can also tell you for sure if she's carrying eggs or not.

