All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Answering your question is briefed in the following three points:
First, inducing an abortion after 120 days of pregnancy is prohibited. Such an action constitutes a form of killing a person whom Allah has forbidden. There is no difference among Muslim scholars concerning the above ruling. But, they differ concerning this ruling if the period of pregnancy is still less than 120 days. However, the preponderant opinion is that it is forbidden to cause an abortion before 120 days although this does not constitute a form of killing a person because the soul is still not breathed into the fetus. So, inducing an abortion in such a case is forbidden since the fetus is giving rise to formation and the soul is breathed into it, and stopping that is a form of destruction of progeny.
Second, one is not allowed to marry the woman with whom he has committed Zina (fornication or adultery) unless she repents and delivers the baby in case of pregnancy.
Third, one who commits Zina is not forced to marry such a woman even after she repents and delivers. But, it is better and preferable to marry her in order to conceal her past and to stop any possible repetition of Zina between them in the future.
Finally, we advise the sister to repent sincerely and to show patience and satisfaction towards what Allah, The Great and Almighty, has decreed. In addition, we advise her to avoid abortion. As a result of such a good commitment to Islam, Allah will make it easy for her to have a good husband.
Allah Says (what means): {And whoever fears Allah - He will make for him a way out. And will provide for him from where he does not expect. And whoever relies upon Allah - then He is sufficient for him.} [Quran 65:2-3]
In other words, Allah will spare our sister from every misfortune and evil and will make every good and benefit possible for her.
As for abortion, it will be another form of disobedience.
Allah knows best.