Do it together. She needs to learn so that she knows what to do when she leaves home and is on her own. Lessons in design, budget and DIY can all be taught here.
It would help if you could provide a Before photo, your budget and some ideas on her tastes/interests so I can help.
Drawers and shelves with bins. Under the bed for storage. Choose a theme that she enjoys but will grow with her for a few years. Then paint a neutral color, using decor and linens for the theme to make it easier to change out down the road.
I second Naomie, or at least let her drive most of the decisions. That way she’ll be comfortable in the room, feel pride and have ownership of her choices.
Bins with cubes can double as headboard or room dividers. ALso you can stack them and make it open shelving for books, bags, folded jeans, t shirts, etc. then add command hooks to top, lay curtain rod on the hooks and hang a coordinated curtain and it is an instant closet. Or put them at either end of a bed that’s on a frame only and hang a curtain rod and curtain between them for a bed that creates a sense of privacy and quickly hides that unmade bed!