If you give a girl a younger sibling, she will learn to be a protector. From the first moment that baby is placed in her arms, she will know it is her's to defend. She is her's to keep from harm and the bad things in this world. She will learn that there is no limit to her strength when she feels that her younger sibling is being threatened. And where she once believed that "girls couldn't be stronger than boys", she will learn she has broken that stereotype herself. She will gain confidence from this. Her job is to shield this sibling from anything that can scare them or hurt him/her. And when the days inevitably come that she just isn't able to do this, her job will be to console him/her and promise him/her that it will all be okay, and it all does turn out to be okay. Because part of her role is to always be honest with them, except for when it may hurt. And then she risks her own pain for their sake, and as a big sister, that's alright with her. Sometimes the fear of the truth hurting just too much overrides the instinct, to tell the truth, and morals are compromised for their little sibling, and they find a way to accept that maybe those few times it was okay to keep her from the truth that could've hurt so badly.
If you give a girl a younger sibling, sometimes she will be frustrated by the feeling that he/she is her shadow. She will be angry when she can't have both of her parents at her soccer game because her younger sibling has a game at the same time. But if they hadn't chosen to play the same sport as each other this wouldn't happen. She will feel like her personality is being shared by someone whom she didn't offer to share it with. There will be days when she shows this, and days when she chooses not to say anything about it at all. Her frustration with this doesn't mean she is necessarily angry all the time. She knows she is a role model, a job she wouldn't trade in for all the stars in the sky. Sometimes she just feels like she was once the sun, and now she has to share her light. She will eventually grow to love this about the relationship between herself and her younger sibling.
If you give a girl a younger sibling, she will learn to share what she loves most. Once an only child, she will learn to share affection of her parents and the rest of the family and the friends that have surrounded her. She will share toys, and one day she will be sharing a car. She will maybe share a room, most definitely will share the back seat of the car, more often than anything. There will be fights over little things and fights over big things. She will learn to pick her battles, and so will they.
If you give a girl a younger sibling, she will feel strong, she will be strong. She will know what it is like to have a protective instinct over somebody they love. She will want to take care of them until she can't possibly do it anymore because they don't need her to anymore. Her desire to continue helping them learn right from wrong will never fade, but it will be time to hang it up because she will have taught them all they can know about this. She will never want to stop holding their hand when they cross the street or giving them piggyback rides or letting them crawl into bed with her when they have a nightmare. And as much as it will pull at her heart when her little sibling is all grown up, her heart will be filled to the top with love, because then she will have not only a younger sibling but a friend.
A proud big sister