Is this natural and is the tenses correct?

Grandmother: "It happened about 30 years ago, but I've never told anyone about it before now. He didn't want me to because he felt very embarrassed. But now he's not here anymore, and I think you deserve to know the truth."

Girl: "He must have been very special. ’Cause I (can) just imagine it must be hard to forgive someone who's done something like that to you."

Grandmother: "It certainly was, but I'm glad I did."

Is this natural and are the tenses correct?

Is it more common to say "I just imagine" or "I can just imagine"?