I found a nice blog on black and red bedrooms:

https://www.interiorcharm.com/bedroom/red-black-bedrooms/

Dark walls, like black walls or red walls, is that what she's wanting? How much say will you be allowing her to have?

On Etsy.

Don’t start in a vacuum! Sure black&red sounds a daunting when you have no direction but I have painted plenty of rooms black! Start with a wonderful fabric and see we’re that takes you! Make it bold and fabulous! A young imagination isn’t as restrained as an adults an there’s a lot that can be freeing by going with the flow;)!

How much fun would this vintage barkcloth be to work with! Very Jetsons!! And this fun floral right out of the 1970’s! So adorable! You needn’t paint all the walls either but I’m picturing fluffy red or black shag rugs and beanbag chairs!

Does SHE have any inspo picks? I think it could be fab.

I love that barkcloth fabric

That room is fab, hollybar. Love how they added pink. It softens the red. Red and black is not my favourite combo but I think I'd like it very much combined with a third colour in almost equal measure.

Is she a girly girly or more of a tomboy?