My suggestion: What about a Spectra Vondergeist costume this year? I would not suggest it for a child though. It is for us adults only!
http://www.toysrus.com/product/index...earchURL=false
The link gets you to a doll, but children are dressing like these Monster High (School) characters apparently. An outfit like this could be put together if you substituited blue in wig and make-up for the purplish colour, adding a lot of black eyeliner, and maybe big, false eyelashes in blue or black. The dress, in a see-through material, (over an outfit less revealing), might require a lot of shopping around, or an Internet search.
My Internet search would start with: www.costumechik.com
I have dealt with them satisfactorily and they now have many adult costumes on sale - clearance.
I spotted blue and purple wigs at: http://www.thebreastformstore.ca/wig...ito-flirt.aspx