What should I realistically do as an aunt when I’m worried about my niece?

I’m looking for practical advice on what I should do in this situation. I care a lot about my niece (10F), but I’m not her parent (I also don't have any kids myself) and this is going to not be an easy situation if I decide to do something.

My older brother is her dad. We are 5 years apart. We’re not very close and have very different personalities and values, so I’m not someone he would typically take advice from, especially about parenting. We try to stay cordial, but there’s definitely some distance there.

My niece lives in a large, busy, blended family. She has three older brothers (each with different custody arrangements in different households) and two much younger sisters (both under 3), with another baby on the way. My SIL owns a dog grooming business and my brother is in the Army Reserves, a firefighter, and currently getting his master's degree online in one year. (and he just finished up his bachelor's degree online too, so this has been a constant time consideration for a while now)

Over the past few years, I’ve noticed some changes that have made me unsure how to best support her:

• When she was younger, she was involved in activities like pageants, dance, and other extracurriculars and got a lot of attention, but since her younger siblings were born, she no longer participates in activities, seems to get less one-on-one attention, and is often expected to help with the younger kids.
• She doesn’t have her own private space at home. She sleeps in a converted den area that they boys walk through to get to their rooms. The 2 littles are currently in pack-n-plays in my brother's room still. (no clue what they are going to do when thew newest one arrives)
• She struggled with online learning during COVID; yes she was in prek/kindergarten/1st grade era and yes they still did online learning during that time.
• This past year she was enrolled in a fully online program again. From what I understand, this hasn’t gone well. She is currently failing 3rd grade, will have to repeat it, and has been described as testing closer to a 1st grade level academically.
• During the school day, she is usually at her mom’s workplace rather than in a structured learning environment, and it doesn’t seem like there is consistent supervision or support for her schoolwork. At times she also helps watch her younger siblings during the day (they are not in daycare).
• She doesn’t seem to have much regular interaction with kids her age and has said she feels anxious around other kids.
• I’ve personally seen situations where her parents respond by raising their voices or being very strict when she seems overwhelmed.
• She has had some behavioral struggles in the past (diagnosed ADHD I know about) and has also experienced a traumatic situation that required therapy.

I’ve also spent some one-on-one time with her that stuck with me.

Last summer, she stayed with me for a few days and had a hard time regulating emotions, seemed very anxious about getting in trouble, and seemed surprised by calm, patient responses.

Yesterday I was able to spend an afternoon with just her. She told me directly she is failing school and is very worried about it. She said she was tested and scored at that 1st grade level and says that test must be wrong. She also shared that her family will be at the beach during the end of the year state test and is worried she's going to get in trouble for not doing the test (they have to go in-person for that) and says the principal said she had to talk to her mom.

There were also a couple of smaller moments that stood out. When I bought her some inexpensive art supplies, she seemed genuinely surprised and kept asking if I was sure. Later, when she saw a shaved ice truck, before I could even acknowledge it, she said she wasn’t going to ask for anything because we had already had ice cream, in a way that felt more cautious than I would expect for her age.

She’s a kind, creative kid, and I care about her a lot. I know I’m only seeing part of the picture and I don’t want to jump to conclusions or create conflict unnecessarily.

At the same time, I feel unsure about whether I should say something or just focus on being a positive presence in her life.

What would you actually do in my position?
Would you bring concerns up to the parents, or focus on supporting her directly and staying out of it?

Would you risk the already rocky relationship with your sibling and SIL? I've tried sharing my concerns with my mom but she says I'm reading into it too much. I can keep trying to share those concerns but my mom seems to think it's not that bad.

TL;DR: I’m worried about my 10-year-old niece’s academic and emotional situation, but I’m not her parent. What’s the most appropriate and helpful thing I can do as an aunt?