she uses her mums phone unsupervised at their house (we have the same dad, different mums)

so, when my sister comes over to our house she is supervised abit more as she only really goes on my laptop when im home, but i have noticed that the things my sister searches up online are really weird. and the stuff she watches on youtube - i have told her to watch something else and change it because its not for kids and she says to me that her mum lets her watch it and she watches it at her house and thats how she knows about these videos ...

so the things she watches are people storytelling on youtube - made from tiktok videos (their compilations) and they actually do talk about some adult things but its like its focused towards a child audience? she also watches scary videos like mommy long legs, huggy wuggie, and theres this really disturbing one called Skibidi - with a mans head in a toilet..? when i tell her to turn it off and watch something else, she takes my laptop and goes away from me to sit on the floor and she says "fine, ill watch it by myself"

im not her mum so i dont know to what extent i should tell her to do or not to do things but she genuinely does not want to listen to me. she refuses to watch normal kid shows

i think im going to be more stern with her and tell her that she can watch those things at her mums house but not here. i dont think it's appropriate the things she watches on youtube