Dear Ruby,
Has the woman employee has given official information to the company on her pregnancy? Is there any law that stipulates notice to the employer in case of pregnancy? If not, then officially you do not know about her pregnancy. Sooner you came to know about her pregnancy, you should have told her to rush to India to get married. 1-2 months after return, she can officially communicate to your company about her impending delivery. Pregnancy can be considered as "premature delivery".
Of course, for the machinations like this, you need support from the top management. It all depends on her level in the organisation, how important this woman employee is etc. Otherwise, option of telling her to quit the employment always exists!
Thanks,
Dinesh Divekar