They instinctively think there’s no way this dirty little girl is the miko so it must be the cleaner ‘prettier’ sister
It says in the novel that the sister is so pretty that the parents can't believe she's their child. Everyone in the village wants to support the family because of her (financially).
It also says they don't feed the MC much, hoping she will die. She goes to the forest, never meets monsters and always finds a lot of food.
The villagers throw things at her claiming she's not fit to be related to her sister but it doesn't hit her, making them think she's creepy. If the mother tries to hit her, the mother falls and if the father tries to kick her a snake conveniently passes by him, so he backs away and falls. So no one wants to go near her thinking that she will bring them misfortune or that she's a plague.
Interesting
Can I get the novel link? I tried looking up the name but i only got manga results
The translator didn't make a page for it on novelupdates since they weren't sure if they would pick it up: https://shiroritranslations.wordpress.com/2019/07/16/miko-is-me-1/
They got the wrong girl..... those parents are shit heads!! (╬￣皿￣)凸 But the good thing is she is in a happy place and sooner i shall celebrate the day when she is realized to be the real miko.... with the parents regret abandoning her
(=・ω・=) mauhahahahahahha!!