Amelia is Wendy's BFF since the first grade, and she's always there for her, even if she can often be brash and abrasive. After 9/11, Amelia is totally there for her bestie and holds her when she's crying—but she's also the only person blunt enough to call things as they are, and she's the first person in Wendy's life who says straight-up that her mother is dead:
I'd really like to get to know you more, the tangerine peel said. It's just so fascinating having a friend whose mother got killed.
The second she said it, she gasped. Seth looked up from his sandwich. Oh my God, said Amelia. It just came out.
It's okay, Wendy told Amelia. She felt relieved that someone said it, finally. (6.54-56)
Instead of being offended, Wendy is relieved that it's finally in the open. Amelia isn't trying to hurt Wendy; she's just utterly honest, and that's something that Wendy needs with so much uncertainty in her life right now. Even when Wendy moves all the way across the country, Amelia continues to call her and keep her up to date on the latest news, telling Wendy all about her sexual exploration with the new boy in class and revealing the fact that Kate and Josh are dating each other. These girls have no secrets from each other—and that's just the way they like it.