7 year old glued to the laptop

Firstly, I understand it is not my place to say anything, but I am concerned.

My niece is 7 years old, 8 in May.

From the minute she wakes up, she will sit playing Roblox on her laptop, up until my sister sends her to bed at night. She was bought a tablet for Christmas that she barely even touches, but when one of her siblings is using the laptop, she will play Roblox on her tablet. If she believes it’s “her time” to go back on the laptop, she will kick up a fuss until she gets what she wants. She’s the youngest of 6 children.

I am concerned about this because the only time she isn’t glued to a screen is when she is asleep. There are days where she doesn’t change out of her pyjamas from the night before, brush her hair, nor brush her teeth etc because she’s woken up just to sit on the sofa, countless times I’ve had to tell my sister that her child doesn’t smell pleasant because she’s not bathed or brushed her teeth! She has very poor eye sight and has to constantly wear glasses, and when she doesn’t wear them, she blinks rapidly. My sister and her family are not disgusting people. Her house is lovely, and they are very clean and tidy otherwise.

I have two children who are 5 and 8 who love the outdoors! They are always doing practical things, and I limit their screen time as much as possible. When we go round, which is most days, their cousin barely plays with them because she’s attached to the laptop. I know I shouldn’t compare our children, but they seem to be very different in nature.

I am very worried about her. She never leaves the house other than school, her hygiene (especially oral) is suffering, her eyesight is poor, and not only that, Roblox is an online community so she could be speaking to anyone on there. As I said, it’s not my place to say, but I’m concerned about my niece.

How do I speak to my sister about this without offending her or sticking my nose in too much? I know I would be offended if someone gave their opinion on my parenting schools, I just think in the long run my niece will suffer greatly if this is how she’s spending her childhood...