Yes you should forgive her. She made a mistake in the past and she has asked Allah for forgiveness as well. If you love her then you should forgive her for the sake of Allah, and lead her and yourself towards becoming a better muslim.
Many humans make mistakes in the past, and some non-muslims become muslims after they realize their mistakes and find themselves on the path towards Allah. Their past mistakes may even lead them to become better muslims than any of us. we don't know, only Allah does.