What did she see on YouTube?
I'd be very curious about that. Choosing stuff yourself online is a highly rewarding dopamine fix, especially with big media giants like YouTube, Facebook - even MN lol! She's up against it - as are all humans with screens...we accidentally got our 3y old at the time, addicted to the ipad (they'd just come out) and my god the screams and anger when it was removed completely from his life once we understood just how bad it was, was pretty horrific. But he calmed down very soon and life was way easier after.
Go deeper, what is about YouTube that she so wants?
If it's because they're watching a show on there, then I'd consider allowing her to watch exactly what it is they're watching so she can continue to bond with them and be part of things. But very fixed time limits and exact details.
However if it's make up tutorials or weird toxic shit and mindless scrolling, then of course not.
YouTube actually has some great educational resources for kids. it's worth checking out. I wouldn't demonise YouTube completely.
She's going to have to navigate her friendships without access to YouTube by the sounds of things so help her work out what that looks like and how she does it without needing to play the 'keeping up' game.
I'd be curious to know is she angry about not being able to see whatever the content was because she wants to discuss it with her friends or is it because she just wants full personal control - or maybe a bit of both. It may not be too early to explain just how addictive places like YouTube are...
And I'd just go a bit deeper about the obvious frustration. But hey, that's me. I like to support my kids and probe, not punish them unless there's a clear reason. Underneath anger is another emotion... find out what it is.
And I'd just laugh and say, yeah you know what, sometimes I'm a shit mum, but on this occasion when I said no, that's definitely one time I wasn't being a shit mum. No one is perfect... so I can take it and then just laugh. She's 8.