So basically she doing it on purpose to get her closer to older brother by making herself fall from stairs intentionally which is a very stupid move for me.
If she wants get closer to him, she shouldn't take extreme move like that because that will cause her brother feel guilty from what he said before.
Actually, that kind of damage she get from that usually results in coma or permanent memory lost due her tissue brain damaged so badly but she still remember some of her memories which is weird for me.
I have same cases when my nephew was falling from 2nd floor stairs when he was walking around but he get stumbled and falling from stairs with head 1st and he lost so much blood, we were very worried about his conditions and we take him to ICU immediately. His life is saved but we got worst news : he lost all his memories due his brain got severe damage and he cant remember himself at all which is a huge blow to his family.