Well, obviously. Unless your hair actually looks like hers..
I'd say pigtails.
buychina Amazon
Most cosplay wigs are meant to act as regular hair..so...yes.
Try ebay.com, they have a large variety of high quality cosplay wigs.
Hello Cosplay
Hello Cosplay or Amazon
You can find a Riversong cosplay wig at various online retailers such as Amazon, eBay, and specialty costume websites like Etsy or CosplayWigs. Additionally, stores that focus on cosplay and anime merchandise may carry similar styles. For a more customized look, consider checking out wig retailers like Arda Wigs or WigIsFashion, where you can find a range of colors and styles to match Riversong's iconic hairstyle.
This is all I can find: http://www.cosplaymagic.com/nashabcowig.html
Try looking up different cosplay sites and ebay.
Suggestions:EbayAnime cosplay sitesYour local anime storeYou can make it yourselfOr find a store online.
Look for wigs on Ebay. Or take a wig from a wig store that is the same color and style it yourself. www.wonderlandwigs.co.uk also do some good quality anime and cosplay wigs. Or standard wigs in a rang of colours which you can then style.
Are you going to a anime convention? You don't need to cosplay. It's not a must... unless there is a rule for that particular convention.You could just wear a wig and a cute outfit, and say that the character you cosplay would wear this too. Or just wear something similar. You don't have to look exactly like that character.