She will stop eating 2 or 3 days before she starts to dig (in my experience ... which is limited)
They get unbelievably huge before laying, my girl looks like a bag of marbles, keep her warm and when she stops eating tape paper or something around the enclosure so she has some privacy.
u cud try putting her in a seperate layin container make sure she cant get out then if shes ready shell have nothing to do but lay, some chams go over 30 days before they lay tho, keep an eye on her make sure shes drinkin, she will be restless when shes ready to lay , movin up and down the cage , this wud be a good time to put her in a layin container.