This would probably be better in the wig forum.
If I where to go about it myself I'd buy a pastel blue base wig and add pastel tones of pink or purple into it.
Something like Arda Wig's 'Candy Striper
' in Harmony looks similar to what I am assuming you'd want out of the color?
That is I am assuming you want a sort iridescent multi-tonal effect.
Since her hair is essential large blobs I would avoid blunt edges and use spray to round off the bangs and ends of the wig. Possibly use wire hidden inside the hair to made individual 'drops' coming off at the ends.
I'd definately say move this to the wig forum where people may be more knowledgeable.