If and when you think that a female turtle or tortoise may be gravid, you can take her to a vet and have an X-ray film taken to show whether or not she has eggs in her. The radiation dose is low and will not hurt the mother or developing eggs.

In the species with which I have had experience, eggs are usually laid within 5-8 weeks of a successful breeding. It sounds to me as though your pair IS large enough for this to be possible this year.