I don't think Peter ever really forgave Susan, not after she reduced Lucy to incoherent tears the last time that Lucy ever tried to talk about Narnia with her. The Lion knows, if Susan hadn't been a girl I'd have punched her for it myself. But, perhaps because I still remember how beastly I used to be, after my initial anger with Susan was spent I could understand where she was coming from.
Susan and I, we're different in many ways from Peter and Lucy. I don't think they could ever understand how anyone would want to forget Narnia, or to move away from what we were there. Peter always thought that the pain of losing Narnia was more than equaled by the joy of having been there at all, and Lucy…well, Lucy trusted that she'd find her way back in time. It was Susan and I who had the hardest time with Narnia. I think that Susan loved it too much, she didn't know how to bring the truths of Narnia back to England because for her Narnia was entire and indivisible unto itself. The pain of losing everything that Narnia meant was too much for her to handle, she had to through it all out to keep herself intact. As for me, well, Narnia would always remind me of my worst failure. And while I might want to forget my betrayal, to do so would cheapen Aslan's sacrifice, and I could never bring myself to do that. For me, remembering Narnia was as much a penance as it was a joy.
So I could understand Susan's bitterness, her anguish at that loss and her desire to expunge it from her memory. I just prayed that someday she'd be able to look past her injured pride at being forbidden Narnia, and remember who she was as Queen. And I hoped that one of us would be there for her, on the day when all her carefully crafted barriers came crashing down, so that she'd have someone there to help pick up the pieces and remind her of who she could be.
But all this musing isn't going to get Peter and Lucy and I down to the train station in time. Susan would have to be on her own today, the rest of us had things to do for Narnia.