Help for Anxiety

So guys my sister (8F) has quite a bit of anxiety. We are kind of in a toxic environment and she was very defiant, reactive and defensive. However I have been able to change that by separating her from this environment as much as I can and she is a happy calm kid most times. But whenever something does not go her way even the teenie-tiniest thing, she gets into an anxiety loop where she isolates herself in a room or bathroom, does not communicate, except silent treatment,  yelling and snappy backtalk.

Another characteristic of these loops is that she thinks everything is going to go absolutely downhill from here and that she has to fight everything. Like in her lil head she KNOWS everything is only bad, if ykwim. So when this happens, if I try to cheer her up by making her laugh or giving something that is her favorite she will say either

1. Nothing good matters because everything is from a bad feeling 

"You don't even care"

"They don't want me to be happy" etc 

or 

2. Everything is bad because everything in life will be bad.

"You are not actual going to let me do that [nice thing]"

"I will be late for school"

"My friends will not call me to play."

Now when 1. happens i ask her "why" and she replies with something from 2. And then when the good things in 2. actually happen instead of acknowledging it she moves on to another thing like "So what I know [nice thing] will never happen. And this loop continues till she hits something that will actually not happen like mom come home 2hrs early from work and I try to explain to her how its ok even if it doesn't happen but she replies with "I KNEW" and gets more angry and reactive. Now the only solution I've discovered to this was somehow making her laugh and  forcing her to watch TV. She likes TV so much that it overrides this whole thing and everything becomes normal, she talks normally, laughs and plays, etc. The only catch is she gets snappy if you try to discuss her previous behavior with her and if you try to discuss it with her at some other time when she is normal, the loop restarts.

But we can't do this too much as she was mad addicted to TV and our mum and I had to spend a lot of effort on that addiction and now she is allowed TV only once every week

If any of y'all have anxiety or kids with anxiety pls reply. I have not been able to teach her grounding because i can't do that without associating it with the anxiety and as mentioned i can't talk to her about the anxiety.

If anyone has any ideas pls share 🥲🥲