This takes place between Prince Caspian and Voyage of the Dawn Treader, book-canon. I own nothing.
"Are you angry?"
The sunlight falls hot and bright over the floorboards as Lucy asks that question hesitantly. She's just started talking about Aslan and Narnia for the umpteenth time this month, talking about how she can't wait to go back. Bouncy, buoyant, her cheerful words so piercing that Susan can feel them clawing the marrow from her bones. She can hear the way they scrape, like fingernails on a chalkboard, a hideous sound that just reaches inside of you and refuses to leave.
Susan looks over at her and smiles, that serene, sedate smile that cracks her skin like old silk. "No, Lu, of course not." She runs her brush through her long hair again, hacking at a snarl more viciously than usual.
Susan was always a better liar than Lucy. Lucy can not see through lies because she never had to, because no one ever asked her to; she is satisfied with this lie and smiles contentedly, her brightness scorching the flesh from Susan's bones.
Colder, quieter, older, Susan is angry about a good many things, though for her sister's peace of mind she'll never say so. The teachers who deem her stupid. The girls who whisper and point at her because of what her siblings say and do. The boys who pinch, tease, prod, holler and whistle, as they never would have dared to do in Narnia, where her body was her own and everyone knew that, everyone knew that the body of a female was not their property and deserved as much respect as a male's. The ones who see the boys do this, and look away, or else blame herfor what others do, glaring and judging and condemning ('Little hussy' 'Who does she think she is?' 'Beauty is vanity, wretched girl; you will never be good in the sight of the Lord until you humble yourself!').
She knows this isn't right, but no one else can see that. Susan is the only one who sees a lot of things.
Your words painted you as a kindly God, though not all the time. (Too old for Narnia at thirteen) Your actions showed you as cruel and capricious. (Soon to be known as 'No longer a Friend of Narnia') One hears your words and sees one thing, but looks at the way you behave and sees something entirely different. (Soon to be condemned as 'obsessed with lipsticks and nylons and invitations', and never have her story asked. They, these others, they will only ever judge and condemn.)
You were never tame. You were never reliable. You never listened. I don't know if you cared about us and Narnia at all. If you did, you chose odd ways in which to show it. Perhaps I am not as discerning as the others. Perhaps you chose to reveal more of your mind to them than you did to me, always the last you showed yourself to.
That's right. I was always last. I was always the last one to see you. Lucy was always first, and one of the boys was second, then third. No matter what the circumstances, no matter what I was feeling and thinking, you always showed yourself to me last.
And now, I'm the only one who can see past you. Our memories of Narnia slip out of our hands here like wine spilled from a glass, but I am the only one who can look forward, and not behind. I'm the only one who can live here like you told us to.
Susan and Lucy are different in their anger.
Lucy's burns bright and hot like the roiling, stormy core of an Earth-star flaring outwards, passionate and searing. Susan's is cold as the winter's bitterest chill, subtler but more than capable of turning extremities blue. Lucy can not hide her anger, because she never had to, because Narnia never condemned a woman's anger and she's not old enough on Earth yet to start being berated as 'unwomanly' when she raises her voice; here, she's just 'a brat.' Susan can hide her anger beneath a smile, fooling everyone, and all the while it simmers, boiling just beneath the surface—she doesn't feel nearly as 'gentle' as she used to, not when the world is gray and dull and no one understands and she just wants to scream her truth to the world.
She doesn't feel 'gentle' when she knows she's been abandoned to this faded place, this shadowy land, and forced to make her life here, and is told she will never again return to the warm, vibrant place, so beautiful it made her heart die in her chest, the place where once she was a Queen, beloved and respected.
Lucy's anger burns out quickly, and she soon forgets. Susan never does. She wishes she could be like Lucy, who forgives and forgets and loves so easily. She wishes she could have the sort of love and faith that blinds her to the truth staring her in the face and instead leaves her to live in a state of half-dead bliss, but she has never been so fortunate, nor so warm and malleable for that, and Susan Pevensie is a girl for grudges.