1. Abortion is forbidden. A child is a human with a right to life regardless of how it is conceived. However, some scholars allow abortion in this situation if keeping the child is psychologically or personally traumatic. It is certainly not a requirement to abort the child.

2. "No man may marry her after that" - who said that? Yes, some people have some backwards ideas about virginity or purity or marrying a woman with kids, but these ideas are from people, not Islam. If the woman wishes to marry, inshallah she will find the right husband. Maybe she would not want to be married to someone who thinks in a wrong way. 

Allah is merciful and just. It would not be merciful or just for Allah to punish the victim in this situation by forcing more consequences on her after the first trauma.