I liked Kill Ari 1&2 for them and Hiatus 1&2. Plus all of season 4 was great as Gibbs is really concerned about her obsession with the frog! I also liked the little flashbacks we got in Judgement دن of them on an op, they were undercover!
i think the most we found out was definitly in season four, i mean, and the end of season three, cuz, she didnt know that gibbs had had a kid and wife, i mean, it was just astonishing, really