The case in this episode wasn’t much. Just a backdrop. They showed more that the new Sec Nav is basically a good person who takes her responsibilities seriously, who respects Gibbs, Vance and NCIS and who was kind to the newcomer when the newcomer needed someone to be kind.
More importantly, they showed the newcomer belongs. Replacing a longtime lead on a show is difficult and here, Ziva was a replacement herself. While the show it all goes back to decided to replace their lead with the polar opposite in season eight and making him the anti-Mulder before he was a real character, Ziva was her own person and far more interesting than Kate (never liked Kate - thought she was a, pardon the pun, shrew). Ellie seems to be her own character too. Physically Ziva’s opposite - Midwestern blonde with a wedding ring - she had her own traits, quirks and personality that made her interesting. Didn’t even seem to have the NCIS requisite troubled parental relationship. All good.
She was smart, she held her own against the boys and her quirks worked. So far so good. If she’s eating in autopsy by the end of the season we may have a problem but I like Ellie.