We literally see one panel later that the girl standing near the railing is indeed Nami.
Also, Lilith appears standing alongside Usopp and Chopper, while the silouette is standing alone.
This, together with the fact that Lilith wears a black very distinguishable jacket, while the silouette doesn't.
It also would make 0 sense to draw there Lilith while Nami and Zoro are the two talking in the panels.
Here Oda has to draw symbolically the crewmembers and the Sunny being in danger, and he choses to do it by drawing a single person.
To be fair, being a very little drawn silouette, we can't tell with perfect precision who it represents, but being Nami, Usopp, Chopper and Lilith the ones on the ship, is clear that Nami is by a very wide margin the most narratively important of the 4, and also the leader of the group while also being the one who rules the ship for the most of the series.
And so, by logic, this is Nami, cause Lilith here wouldn't hold any meaning, on a narrative and emotive level.
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And yea ofc, that's an old one, I am sorry for being too stupid for you. I brought you some useless evidences, but it's clear you already have everything figured out, lucky you!