I'd like to point out 2 things about the Marvel movies, including this one, that occurred to me:
-What, exactly, is Susan Storm's character at this point? The closest I can figure is "over-protective" of her idiot brother, but considering she's had to evolve out of her "token helpless female" role over the years it could really be anything, which I think may make it reasonable for Mara to not need much background info.
-Many of the Marvel movies, even the "in-house" Avengers canon ones, contain ridiculously dark themes and scenarios, even if they often appear light-hearted on the surface: the post-9/11 undertones of a ravaged and frightened New York; Tony, billionaire tech wizard, blasts away deranged war veterans turned suicide-bombers at the end of IM3; Winter Soldier biting down on a mouth bit before being electrocuted and mind-wiped; Banner talking about trying to blow his brains out but the Hulk wouldn't let him; a female scientist gets incinerated by Scorch in Agents of Shield. Yes it's not constant gloom and angst the way other "mature" hero movies strive for and I'm not looking forward to something intentionally tagged as "grim n gritty," but I think Marvel tends to get away with a lot of disturbing material that not many people point out.