You just need to find ways to cope until the screaming ends and never, ever give in again.
It will stop eventually even if only because she is too tired or too hoarse to continue.
You can't give in then and say because you stopped you can have whatever it is.
It has to be a firm unchanging NO means NO.
She will probably escalate and try harder for a fair few times at first, but she will learn it doesn't work any more.
I know it's distressing to see/hear/deal with, but if you'd put your foot down when she started this, it wouldn't be so bad now.
You taught her this works.
Maybe leave the room, or put on headphones and listen to music?
You create this problem and entrench it in her behaviour every single time you give in.
You have to just endure the screaming because bad as it will be at first stopping it at 6, just imagine how hard it will be if she is 16 and still using this as a technique when she's too big for you to deal with if she gets physical.
Maybe let your other child who shares a room sleep in another room for a few nights so she doesn't have to be in the middle of it?
Or could she stay at a relatives house for a few nights?
It's really unfair on her.