Why not use some of her art work on the walls, in different size and style frames (natural, black, white & silver) - you can pick up some cheap frames in the op shop and the bargain stores - just buy some spray paint, and have fun - let your artist help....... you can even photograph some of her art work and have it blown up to poster size - the brighter the better. I'd suggest painting the walls white, with maybe a feature wall a timber bed head - one with a book shelf would be great - a double of course - the room is big enough. A rug to anchor the bed and some funky cushions. An Eames DSW white retro chair and a small white desk with some floating white shelves for odds and ends.... I'd probably get a white roller blind for the window, and paint the door, wardrobe doors and skirtings white, and a lovely large retro style light fitting in the middle of the room, or a hanging pendant next to the bed. A small bedside table - try Ikea - they have a great range, and not too expensive, you may even be able to get a great bedhead there - she sounds a very practical girl, so no frills. You want a young, fresh, modern look. Place the artwork randomly, in groups, on the walls - hang paper cut outs on the walls with blue tack, to see the effect, before you put up the art - Your artist could help with that too. What's her favourite colour??? Does she have any hobbies?? We need photos and more info.... What a lovely step dad you are!!! Good luck. I hope I've helped...

I would go off the code numbers for these first, as surprisingly the names can change in different countries.

Since your home is a cottage, I feel mirrored is a bit modern but encaustic tiles would be gorgeous, something subtle would be lovely, maybe like this https://tilehaus.co.nz/products/austinmer-grey-encaustic-look-tile?variant=40293687460040&currency=NZD&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic&utm_term=&utm_campaign=gs-2021-03-24&utm_source=google&utm_medium=smart_campaign&hsa_acc=2523824507&hsa_cam=12611051513&hsa_grp=122872652867&hsa_ad=509293891322&hsa_src=u&hsa_tgt=pla-293946777986&hsa_kw=&hsa_mt=&hsa_net=adwords&hsa_ver=3&gclid=CjwKCAjwh5qLBhALEiwAioodsyZ9Y4FT2OEtSdHfzucjzV59JkZ-Gj3npqr9Q3HQv3GHcgOpw4orjhoCf7MQAvD_BwE Granted I do just have the colour swatch not a brush out or test pot, but to me Whisper White is looking very cream and I'm not seeing any green undertone Are you sure this is what you are looking for? Perhaps try Lyttelton Quarter.. or even better, choose your tile first and select the paint to work with the tile :)

In your example I’d paint the trims the darker colour but have the whole room the darker colour not just a feature wall.