I think that the sexualisation in Jesse's early scenes is a misdirection of the audience to believe that she's just a love interest for Derek (to make it clear to the audience that the show won't go in an S/D direction and turn it into a standard nuclear family)

*nods* Mind you, I suspect that part of the hostility towards Jesse early on is less due to an objection to her introduction on the grounds of sexualisation of a female character and more due to disappointed shipper rage, because quite a lot of S/D fics had been written during the hiatus, and I think as opposed to some 'ships, this was one where its partisans really expected the show to go there.

Complications is only the third episode Jesse appears in and already showcases both how ruthless and how traumatized she is, so the show goes on to point out there's more to her than Derek's love interest pretty quickly.