for me, foreshadowing her death three times in tasm1 was enough for me to conclude, on the balance of probabilities, that she will die in tasm2. foreshadow three times only to stall, foreshadow more in tasm2, then finally have her die in tasm3? that's bluer than electro's balls.
also, we know peter starts off on top of the world. so what better way to knock him down a peg than to kill gwen? sure, he could get knocked down some other way, but recall foreshadowing in tasm1, recall that broken promise.
furthermore, it makes sense for a 2nd chapter in a trilogy to end on a downer (especially when it starts with happy-go-lucky peter), and to have the third chapter deal with the fallout. who would want return of the jedi to end with han being frozen, kidnapped, and luke amputated and told he's hayden christensen's son?
the sinister 6 stuff and general world-building occured after initial plans for a trilogy. so i also think it is sensible to conclude that tasm3 will be peter vs. the green goblin. we also know tasm4 is a spider-man movie, and happens after a solo 6 movie, so the setup is there for the former to be an event film.
all these reasons do not prove she dies conclusively. but, for my standard of judgement, do prove she will beyond a reasonable doubt.
there are other tid bits that support her dying, such as her clothing, certain allusions in quotes from filmmakers and the cast, emma's contract, today's headline about "death", etc.