You should start with a wig that's already parted into ponytails --that'll just make things a bunch easier. Look for something like the 6th from the bottom of this page:
http://www.cosplaysupplies.com/specials ... tion=WIGS4
in either white/silver or very pale pink or lavender. You can adjust the position of the ponytails to sit higher on the head, but at least the hair will already be sewn in the right way for the style you want.
Then you can use heat & various sprays to curl & shape the hair.