"Chosen Sister" is published by Wild Child Publishing. They put out an eclectic bunch of books. I've had stories in a couple of their anthologies, so I gotta like them.
Buy Chosen Sister in ebook format for $5.95 at Wild Child.
When the Gold Wizard comes looking for the Child Warrior in Reina's village, it's no surprise he's only looking at the boys. However, when the wizard magically selects her younger brother as the warrior prophesied to defeat the Red Wizard, Reina has mixed feelings—jealousy and concern. Austyn is only six.
Allowed to accompany her brother, Reina soon finds they're in deeper trouble than she thought. The Gold Wizard's fake beard is ripped off by attacking harpies, revealing he's only seventeen, not to mention his magical demonstrations tend to go awry. Unfortunately, with the Red Wizard's harpies and snakewolves on their trail, finding a new (and better) wizard mentor is hardly an option. If anyone's going to find a way to track down the elusive Sword of Chivalry for Austyn and get him into the Red Wizard's castle to fulfill whatever the obscure prophecy insists must be done, it's got to be Reina.