A flat plastron and narrow tail would indicate a female, if the individual is sexually mature. The male will signal interest in mating by nipping at the shell or upper neck of the female. Provide the largest accomodations you can, and create the tropical rainforest environment described on the Care Sheet . See an example of a 6'X4' breeding vivarium here , and another view here . In addition to the usual swimming area and land area of basking rocks, your female will require a soil area in which to deposit her eggs.
Some breeders mix the soil with clean sand.
A large outdoor enclosure is best for a breeding pair. Of course, the temperature requirements must be maintained. Along the equator, temperatures and sunlight hours do not change much during the winter. The tropical rainforest experiences a dry season, however. As ponds, marshes, and rice paddies dry up, wild C. amboinensis would burrow and estivate during this period of low rainfall.