That's a great idea!  Something like this would be so cool.  Very HP-ish. 

Some more ideas:
-You could fill a jar with gelatin and label it "Floo Powder". 
-You could make her a clock kind of like the Weasleys.  You could put her face on one of the hands and instead of numbers around the clock you could have "Home, Lost, Prison, School/Work, etc.".  That would be really cool!
-You could decorate a notebook or journal with pictures of the characters
-You could make Harry Potter stationary

Or you can buy a large mirror -- and make a design around it with the pieces of paint samples eg. wave like pattern around it.....or something similar to this pic --- depends on how many paint samples you have & if you don't have enough you can just use blue pictures cut out of magazines and use them around to fill the spots.



 

Ooh, that would be cool.  What would I use to stick them on?  Mod podge?  I've never used it, but I've heard of its many uses.