Talk:Toaru Kagaku no Railgun S Episode 17/@comment-7694700-20130802204204/@comment-10753673-20130803010545

The white haired girl is almost certainly a new character named Febli.

Here's her announcement translated by js06:

The original story includes a new heroine named Febli She is the youngest girl to appear so far She looks her age and her speech and behavior are overflowing with cuteness In a way, she may hold the position of the Railgun team's mascot The original story will reveal whether she is an esper or not She has characteristic clothes and always has a piece of candy in her mouth