Although Ivanka Trump did not attend the "Hillary dirt" Trump Tower meeting between her brother Don and Russian lawyer Natalia Veselnitskaya, Mueller is investigating her interactions with the lawyer after the meeting. The LA Times:
Investigators also are exploring the involvement of the president's daughter, Ivanka Trump, who did not attend the half-hour sit-down on June 9, 2016, but briefly spoke with two of the participants, a Russian lawyer and a Russian-born Washington lobbyist. Details of the encounter were not previously known.
It occurred at the Trump Tower elevator as the Russian lawyer, Natalia Veselnitskaya, and the lobbyist, Rinat Akhmetshin, were leaving the building and consisted of pleasantries, a person familiar with the episode said.
Although it was a brief encounter, Mueller is investigating all interactions between Veselnitskaya and members of the Trump. The LA Times is also reporting the Mueller is recalling for questioning at least one participant in the meeting, with no specifics, and that Mueller's team is interested in Donald Trump Sr's misleading claim that the discussion focused on adoption, not on lovely dirt on Hillary.
Obviously, Mueller is leaving no stone unturned in his investigation into the Trump Tower meeting. And considering that the Wolff book quotes Bannon as saying there is "zero chance" that Trump Sr didn't know about the meeting that seems like the prudent course. Which is what we've come to expect from a stable Mueller, whose work to date would qualify as not smart, but genius.