Nami met Laboon while she was travelling with the Whitebeards. She had always crossed the Calm Belt into the Grand Line, so they 'd brought her here with sightseeing intentions.

She was very happy to see him, but there were things she couldn 't say.

'Brook is alive ' is one of those many things.

That 's information she can 't bring up without explaining in half-truths, because telling someone the truth would flip the world on its tide and create a completely different world from before.

So she can 't tell anyone the full story just yet. At least, not while Blackbeard is still in the Whitebeards.

(Even if he weren 't, there was no telling how they might begin to doubt her allegiance when they find out legitimate time travel is possible outside of the Toki-Toki no Mi. And that was the thing-- they may suspect Nami to be the new holder of that fruit, or that Nami knew who the new holder of that fruit was.)