Since she has repented, she should forget about discussing the past unless he brings it up and wants to know. And if he really wants to know, he should be prepared to be deal with the rotten bones he will dig up. Even though they vary in degree, we all have something in our past which we are not proud off. They should be left where they belong - the past and not brought to the present.
Unfortunately, situations may arise that he will hear the gist from someone else. If he likes her, he will forgive.