21-year-old woman helps her mother by shaming 11-year-old kid sister into cleaning her room, saddened to find their relationship changed: 'My sister now hates me, but if it makes Mum’s life easier, I can live with that'

I feel like there's just some sort of paternal instinct that kicks in when it's required. Clearly some people don't have this instinct: some who have no reason to yet because they don't have kids of their own, but there are also some who do have kids who still fall into this category, somewhat inexplicably. But, as usual, that exception also makes the rule.

When you're 21 years old with two kids of your own already, but still have an 11-year-old sister who is also still very much a child, one can imagine where that might set a weird dynamic where you're both an older sibling with that whole dynamic going on but also have a powerful second instinct wanting to intervene and parent your sibling. 

But, still, whether you have your own children or not at that age, at 21-years-old you're still immature yourself, being that your frontal lobe isn't fully developed yet. That didn't stop this 21-year-old from intervening to help her mother with her 11-year-old sister's manipulative behavior, setting the young girl straight with some harsh consequences. But then finding afterward that her intervention may have irreparably changed their relationship and damaged their sisterly bond.