/vt/ - Virtual Youtubers

Sorry in advance if this is the wrong thread for this shit, I haven't touched this website in years and I'm surprised enough that "/morig/" is now a thing, but let me just jump into it.
Long story short after breaking up with my boyfriend and losing my job I moved back in with my mother and younger sister.
The last time I saw my sister in real life, 3 years ago, she was this happy 13 year old kid with good grades and a boyfriend. She liked rap but whatever so did I at her age.
However now that I see her at 16 it's like she's a different person. My mother is like this helicopter parent and doesn't see anything wrong with herm staying inside all day what with Covid on the loose however I see it differently.
First of all her room is trashed, and absolutely littered with cheap wine and posters of this vtuber, Mori Calliope (I had to google how to spell her name after she told me).
It'd be one thing if they were normal posters, but a lot of them are blatantly nigger (the picture I uploaded is basically how some of them look) and you can tell she hasn't had a boy in her room in a very long time because if he saw all of this wigger shit you'd know he'd be cringed out. Again mom sees no problem with this says I liked the same rap stuff at her age.
Secondly I think she's using this girl as a substitute boy. When I jokingly asked her when the last time she had a boy in her room was she just said something along the lines of "dude have you seen western men these days? they're all too tall" so clearly she has no interest in actual guys her age or height anymore.
Thirdly I worry that she's spending WAY too much money on this girl. I mentioned the posters but that's not all. Her laptop that he uses to watch this girl is riddled with stickers of her that say shit like "guh" or just pictures of her blushing or making other faces. Clearly she's obsessed so I ask her what the appeal of this girl is and she says "your boy" well yeah no shit. I obviously wasn't satisfied with that as an answer so I ask again and she jokes again saying "I'll send her a super chat asking her to explain it to you". First I ask WTF is a super chat, she explains it, I ask if she's been sending money to this girl and she just laughs refusing to answer. I know she's just a teenager but I don't want her to get sucked into bad spending habits like this.
Another thing I worry about is that she's skipping school to watch this girl. I don't have any hard proof of this but one day I peeked in her room when our mom said she was doing online school and lo and behold he's watching Mori Calliope. I don't know if she just had her in another tab or what but considering how she used to be so focused on school this seems like a change for the worse to me. Also this might just be a Covid thing but she's gotten shorter and the only time I see her go out is to beat up mannequin skeletons. I don't know if she has any real life friends at all now or if they're all just online vtuber buddies of hers (she mentioned being in a discord for them once).
Should I confront my mother about this or should I step in as her sister myself? Do I even need to or is this just how teenagers are these days? Any and all advice is appreciated.