Gift of the Unmage (Worldweavers #1)

Great things have been expected of Thea, the seventh child of two seventh children, Now, with Cheveyo, a mage [of the Anasazi], Thea has begun to weave herself a new magical identity, infused with elements of the original worlds. But back home, Thea keeps her abilities hidden and attends the Wandless Academy, the one school on Earth for those who have no apparent magical talent. It is there that Thea realizes that her enemies are hungrier and more dangerous than she knew. What's more, her greatest strength may be the powerlessness she has resisted for so long.