Is it sufficient that I verbally forgave the girl whom I wronged, without informing her of the truth, while feeling guilty after 4 years, and must I tell her now?

The rights of people are serious, and repentance from violating them is obligatory. One of the conditions for such repentance is to seek forgiveness from the aggrieved party.

If the right pertains to one's honor, it suffices to supplicate for the person's well-being.

Seeking her general forgiveness is a good thing, and you should supplicate for her frequently and mention her good qualities.

Lying is forbidden, and repentance from it is obligatory.