IMDb can be very biased with its cast updates sometimes, so this might not be true, however it very well could turn out to be true afterall.
IMDb now lists Meaghan Jette Martin as Gwen Stacy... who is Meaghan Jette Martin? She has appeared on House, 10 Things I Hate About You, and appeared in Disney Channel's Camp Rock.
In my opinion, Meaghan Jette Martin is probably the best suggestion I have ever heard for Gwen Stacy. She looks the part to perfection, now it is just a question of if she can act.