I'm [21F] concerned about my sister's [11F] emotional wellbeing, not sure if I'm overreacting

First time posting here, please let me know if I'm doing something wrong. It's slightly long, so please bear with me.

I'm a university student who's usually been away from home for basically the last two years due to school and work. My sister lives with our mother - our father's been out of the picture for the last 3-4 years. Since I've not been home much, I only recently began feeling that our mother doesn't parent her fully.

All her material needs are provided for, but it feels like there's no concrete structure or schedule in the house, no clear sense of rules and boundaries. I also feel like there's a certain lack of emotional connection and communication, which is something that's been a problem in our family as far as I remember. I've suspected for a while that I experienced childhood emotional neglect, and my worry is that she's experiencing the same now.

My sister is a good kid, but one that seems to have been left to her own devices. My concern comes from observations I've made of her behaviour, which include recent and long-term examples such as:

• she's constantly on her tablet, watching Youtube or playing games - like 10am to 10pm with a few breaks in between
• I've seen her making rude comments on Youtube, and seen her on Reddit - not sure which subreddits - though I'm not sure if she's getting into anything especially inappropriate still
• she doesn't seem to have many other interests and seems to avoid them; she's been signed up for extracurriculars before and just refused to do them
• she has friends, but doesn't seem especially attached to them compared to being online or at home
• she rarely seems to be able to go to or want our mother's help for homework or other issues - if she can't do it herself, she'll just leave her homework incomplete unless I ask about it and help
• she's hit the phase where she'll talk to herself a lot, but give closed-off answers when I ask about certain things, ask her to repeat herself because I couldn't hear, and even shut down at certain points as well

The part where I worry about emotional neglect from our mother is that she's a very independent individual. She's more practical, not the type of person I'd call particularly comforting or nurturing. I don't see her connecting with my sister much emotionally - with a few exceptions, there's never much discussion about her interests or hobbies. She'll ask my sister to do something, but won't seem to give her specific age-appropriate directions or particular structure to do it. There isn't much of a schedule in the household outside of meal times. I've seen her working with my sister on reading activities in our native language, and tease her or make comments that I know can feel embarrassing if not outright humiliating as a child.

I've been trying to counter some of her comments and attitude in places, and give my sister advice and support where possible. The thing is I'm also somewhat emotionally stunted and she's withdrawn a lot as well. There's a lot of silence or "I don't know" type answers when I ask her about her feelings or preferences. I know she's getting into that age where puberty hits and all so I could be overreacting, but given my past experiences I'm uncomfortable leaving it as is.

What would be some good things for me to do, if I were acting in a sibling or parent-type capacity? How should I mediate between my sister and mother? Is there other help I can get or give my sister?

Any advice is much appreciated.

TLDR; worried that my younger sister is experiencing emotional neglect due to lack of family connection and communication, and lack of consistent parental structure and guidance in her life.