When Edith is very young, she wants to be exactly like Mary. Mary is brave and kind and always knows how to make things better. Mary knows everything. Mary is perfect.
"No one is perfect, Edie," Mary says. Then she smiles and hugs Edith and adds, "But I think Mother comes close -- certainly much closer than I do."
As she gets older, Edith begins to agree. Because Mary has gone off to school for months and months, and when she comes home she isn't Mary anymore. She doesn't laugh as much, doesn't smile as much. There's something tight around her eyes, like she's always pinching herself in, holding herself back. She won't run around in the garden with Stephen and Edith and Laurie. She won't play pretend.
Mary is lying all the time.
Mother never lies. Mother doesn't play games with Edith and the boys either, but that's because she doesn't want to. Mary wants to, but Mary won't let herself.
Edith doesn't want to be anything like Mary. She'd rather be like Mother.
She takes to following Mother around the house, watching her cook and clean and sew. She begs and begs until Mother takes her to the market and shows her how to find good food for a bargain, how to plan a week's menu, how to stretch a budget to cover six people. Edith loves learning what Mother does, the same way she likes to learn about practical things like furniture joints and piping and what keeps rain from coming down the chimney flue. Mother makes the family work.
Mary doesn't know how to do any of this. Mary never wanted to learn. Even now that she's pretending to be someone else, Mary only shuts herself up in her room and reads and reads and reads, unless she's sneaking out and going places she won't tell Edith or the boys about.
Edith is a good daughter. Not like Mary.
But Mother loves Mary best. Mother is always talking about Mary, staring at Mary when she thinks nobody is watching, cooking Mary's favorite foods, spending just a bit more on Mary's clothes, telling Mary to look after Stephen and Edith and Laurie.
Mary doesn't know how to look after anyone. All she can do is tell stories -- she won't even put plasters on scrapes or hit people for calling Edith names the way she used to. Edith is the one who knows how to be useful. Edith is the one Mother should trust.
Except Mother just tells Edith not to worry and keeps trying to change Mary.
Edith doesn't want to be like her sister anymore. She doesn't think she wants to be like Mother either. Neither of them is anything like perfect. Neither of them pays any attention to her. Neither of them loves her, not really. Stephen and Laurie follow their lead; they think Edith is boring, like the old shoes they kick across their room and never care about at all.
Edith is so tired of being the good daughter. She's so tired of tiptoeing around Mary, of helping Mother hold everything together, of biting her tongue and not talking back to Stephen and looking after Laurie. She wants someone to see her and trust her and think she's important. Just one person. Just once.
When the Witch smiles at her, tells her she trusts Edith to think of a way to bring her family into Narnia, and calls her "daughter," Edith is hers in a heartbeat.