It's not Lulu. I saw who it was in the presentation I attended in Ghent before the PFH, or at least I'm almost certain that the hollyphant footage I saw there included the shot I recognised from the trailer.
Which of course doesn't necessarily mean Lulu isn't in the game, but that specific hollyphant is someone else we'll meet on the approach to Baldur's Gate city.
(Of course, that excludes the possibility that it is Lulu masquerading as a totally different hollyphant, but I did not get that vibe

)