Is it permissible for a chaste Muslim woman, pregnant from adultery with a non-Muslim man, who has two children, to have an abortion?

Abortion is not permissible. The child of zina (unlawful sexual intercourse) is attributed to its mother. The fetus is not culpable for what its mother and the one who committed zina with her have done. The woman must repent to Allah Almighty for what she has committed.