How did she spend her days before losing her vision? It's likely she'd enjoy similar activities now.

Playing an instrument, cooking, sports, games, hobbies, art, writing, etc. - these are all good ways to pass time. It usually takes a little adjustment, and training usually takes more time, but most activities can be made accessible to someone who is blind.

There are plenty of games for blind/lv out there (here are a couple):

https://www.perkinselearning.org/technology/posts/want-more-educational-apps-are-accessible-blindfold-games

https://www.qcsalon.net/en/

What were her interests before she was blind?

For background, I have occasionally mentored younger people who were in a similar situation to me. I could see fine until I was 19. A few years ago I someone who had lost her sight after a brain tumour operation. She was a few years older than your niece and the reasons why hardly matter, it's the same situation to deal with, but she's not alone.

Finding activities should be the least of her problems. She should be amazingly busy learning how to deal with it, particularly how to get around with a cane if she needs one, and it sounds like she does. If this is not happening, make it happen because you can't start too soon. The parents will be extremely protective and that's to be resisted because you don't want to turn out someone who can't cope in the real world. This is leaping ahead, but at some point, once she knows what she's doing, they will watch their young daughter making her way down the street with a cane as cars go past and that has to be okay. I do it daily and while your brain is probably going "she's only eleven" now is the time to learn and she will be fine if she knows what she's doing. She just has to get to know what she's doing. It's a learned skill, it's not magic.

The reason she's bored and depressed right now is that it feels like she can't do anything, and she's understandably worried she will spend the rest of her life not being able to do anything. Being overprotective actually reinforces that feeling because it prevents people from discovering how much they can do. There's no magic to it, it's just learning a bunch of techniques, it's like doing a course, it's just effort, but that effort does have to be put in. In the short term she'll be too busy to be depressed and in the long term it's a process of slowly finding out you can do a bunch of stuff and that reduces your actual reasons to be depressed.

Not doing much activity is amazingly bad because she will be bored and depressed and end up really unfit, which doesn't help anything.

Either way nobody in this situation should have time to be bored. If she isn't collapsing into bed every night absolutely exhausted she isn't doing it right!

These might be for younger kids, but Maxi Aids has toys for blind/vi children. You might find her something that could occupy some time.

https://www.maxiaids.com/toys

I can hardly see shadows and the sun, from birth.

Reading is great. Even if she doesn't want to read a book *today, reading is awesome, I don't know if that's because I'm blind, or me.

Get her outside, if her body can handle it. Swing on swings, climb monkeybars, go down slides, touch stuff.

I know that blind people can ski, horseback ride and do water stuff like swim and dive and boat. Some of that's expensive, I'm just listing things as i think of them.

An instrument is cool. Even one of those little plastic keyboards, just something to learn marry had a little lamb on, to see if she likes it.

Just the internet is a good thing, especially when you're blind.

She's a little young, but working out is good, any type of working out, tredmill, weights, olyptical machine, whatever.

It's sort of weird, and always get advice. Buut think about all the stuff you're sure she can't do, like drive and play baseball. But then there's everything else left that she can do.

Like, when I was 11, my dad took me shooting. And learning how to load a gun and shooting it and holding it the right way made me enjoy an entire day, no matter that I'll never shoot safely alone.

My mom would take e hiking and make me touch stuff and would read me the signs.

My aunt would take me to the mall and we'd walk around holding things.

Ooh, cooking is good.

I've been blind since birth, so it's different, but keep her from being board, no matter what she's doing.

I hope some of this helps.

Knitting and crochet are good creative options