Borrowing this idea from another thread You could use a length of tuille with hooks like that, a clip of some type. Paint them different colors. If you don't want to try attaching a ribbon, you could just drape it (them) along with the tuille. Or use two shades of tuille -- see how that fabric is two prints? Imagine it mainly white with some pink along the top -- just a bit so it isn't too much with the canopy. You can even buy 6" wide tuille "ribbon" at craft stores pretty inexpensively ($3) and use that for any colors. You could make the whole thing just a valance, sill length or to the floor. If you put the bed against that wall, you either wouldn't use a separate window treatment or wouldn't use the canopy there. If the bed is on that wall, you might want to have a chair or beanbag in a corner where she can have a special "private" reading/playing space. The sides of the canopy could be tied back to the walls to give a pretty drape when open and let her close it when she wants.

Take a look at this duvet set as it has the softer colors in it like your design seed. The reason why I'm suggesting a set is, if you are unsure of your own design sense, which you say you are, then take the help from the professional designers who have already put a set together for you. Having the colors in the bedding make it much easier to pull colors together for the rest of the room like throw pillows, lamps, and curtains. But if you want a solid, it's going to be really hard for us to help you judge colors seeing as you say they are off so much in the picture.

You can do it! I understand the need for sleeping space for guests. I like your ideas

Can you show the other walls. Take some more pics. Please. And I’m not sure I’d go gray... would you do something lighter? A blue?