I didn’t forgive someone and I told her that now that time passed I forgive her. Do I have to tell her that I forgive her?
If you told her that “now that time passed I forgive you,” this is certainly sufficient, and you don’t have to say any more. In general, it is better to speak out one’s forgiveness verbally, and not only to forgive somebody in one’s heart.
Sources: One of the main sources for the principle of speaking out one’s forgiveness explicitly is Rabbeinu Bachya (Bereishis 50:17) concerning Yosef, who didn’t fully forgive his brothers. See also Kaf Ha-Chaim (606:11) in the name of Maharam ben Chaviv, who writes that the party that desires forgiveness should ensure to placate the injured party, and to actually ask for forgiveness; see also Peri Chadash, and Mishnah Berurah (606:2).