And the bedding is a pink and white color frame duvet from Serena and Lily,

Do you have any photos?

Sorry, there are currently lot's of pictures of my daughter hanging everywhere. I'd prefer to not show pictures of her room.

if you want to get real help you need to post pictures.
here's some sweetly sophisticated rooms in your colors for ideas

What color are the walls? Or is that something to change?

The walls are currently yellow. However, they can be changed. We're also thinking of wallpapering the ceiling! I'll post some pictures of her room very soon!

Is the pink frame duvet the Berry color? It's really nice.

Hi---I think the wallpaper should be sophisticated both in design and color palette. I chose a gray, with a muted chartreuse, and varying pink hues. I think this would look fabulous paired with the bedding and white furnishings/carpet. A fantastic light fixture overhead. Hope this is helpful. Good Luck!
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Like this use of pink

Natalie: the chandelier is spot on for a tween through teen girl.

Jillbertsch : this is a good medium for a tween and easy enough to flow in to a more sophisticated room in a few years. Large Art decals are an absolute gift for any Mother raising Daughters.

I would get rid of the lime and yellow and either gray tones or brown, and without making it too sterile, white allows you to choose curtains, rugs, etc without having things clash. My Daughter's room has solid pastel pink walls with a white ceiling. We have accessorized with every color under the rainbow in the last 8 years, comforter and curtains took us from 12 to 20. Now she's in her own townhome, but loves coming home on the weekends to her pink room.

Maybe instead of totally redoing your daughters room, you could just add or take away certain details to make a look you want and still have the feel of the room you had before.