How can you tell if your beardie is gravid?

My big female is getting larger and lazier and it feels like she has rocks in her belly (to my untrained touch) and shes not seeming to want to eat her greens unless we hand feed them to her and tease her a bit. However she still eats tons of crickets. shes still active just not as active. she has had the opportunity to have been bred by our male and she has laid slugs in the past, like 15 of them before we had the male.

(note: shes not my bearded dragon shes my roommates bearded dragon, i just feed her and take care of her and love her to death)

Their belly gets huge and looks like a sack of marbles. She will start digging for days before she is ready to lay and her color should lighten up. When she starts to get digging I would put a covered tub with damp soil for her to lay in.

thank you :) i will get her a tub to lay in