Susan Pevensie is still barely a woman (at least in this world) when she loses her whole family in one fell swoop.
In their last adventure in Narnia, her siblings belittled her discovery of lipsticks, and nylons, and called her 'silly' for acting 'grown-up' before her time. But it wasn't before her time, not really.
Susan had already lived a life in Narnia, grown into the Gentle Queen. Susan had seen how people treated women in Narnia, and she saw how they would be treated in her world. Susan knew that to be a queen she would need to be seen as flawless, as immaculate; she would have to be beautiful and bright (but not so bright as to belittle her companions) and she would, above all, need to be pleasant.
Susan was not a girl who saw joy in everything, like Lucy. She wasn't always as forward thinking as Edmund. And while she might have been a born leader, she wasn't a man - wouldn't ever be 'High Queen', looked to as Peter was.
What would you do, in Susan's place? On finally returning to the world from which she came, Narnia's relatively open-minded attitude would vastly outshine early-twentieth century Britain. Far from becoming queen after saving a whole land, she might at best go to a good finishing school and be able to marry well. Susan the gentle, always expected to be mother, wouldn't have the opportunities that Peter and Edmund would have. But Susan was always the best at bettering a bad situation. So yes, she discovered lipsticks, and nylons, and boys. But how different are they to war paint, armour, and soldiers?
Queen Susan in the old world, with blood red lipstick, smoky nylons and pointed heels - court shoes, actually, and don't think the name didn't make her laugh the first time she put them on. Queen Susan had spent her first life as logical, and sensible, and the most serious of the Kings and Queens of Old. So in this life, as an adult all over again, she decided to be different. She learned, instead of a bow and arrow, to use her words and smiles as weapons. She learned to create an army out of suitors, and made her friends into guards. Agnes, librarian, clever enough to outsmart any enemy; Amy, model-turned-governess, so stunning and statuesque people couldn't help but bow to her every whim; Peggy, agent, with a brave soul and warrior's heart; Wendy, mother-to-be, with a kindness of soul to match even Susan the gentle. Between the three of them, was there any wonder Susan didn't have time to reminisce about Narnia with her siblings? Would you talk about a fantastical land in your past, if you were so busy trying to make a better world of your future?
The day Susan lost her family, Wendy found her sat on the floor of the family library. Susan wasn't wailing - she'd shed her tears later, but first she had to make plans. She knew where they would be, after all. What was the use of crying? They'd all be in Aslan's country, together; their parents would have finally gotten to see Narnia; Diggory would get to see his magic woods again. Susan was the only one left. So she sat on the floor, surrounded by countless fantastical worlds in books on shelves around her, and was simply smiling as she made a list of funeral arrangements. Not a manic grin - not even the smile of someone trying to hold their tears in with their cheeks, but simply the wistful smile of someone who knows they have far too much to do to spend their time bemoaning their lot in life.
Susan would eventually get to see her family again, she knew that much. And she also knew that in the meantime, she had a lot of work to do.