Lightbringer

When an old wrong leads to war, one girl finds herself in the middle of it all.
For centuries, sealed Gates, protected by powerful magical beings known as Guardians have kept the realms of Earth and Wysteria separate.
But, if a Gate is opened, it allows the inhabitants of both worlds to interact freely, sometimes with dire consequences.
It's been six months since Sara Montgomery's mother died. She wants nothing more than to leave her small town, where nothing ever happens and there are too many memories.
But when an old enemy returns, strange things begin happening-things that just don't happen in this little town.
When her life is disrupted by the Gate's opening, Sara finds herself caught up in a magical war, forcing her to rethink what she thought she knew-about her town, her own family, and even herself.
She and her new allies must work together or both worlds will be lost to a wicked sorceress out for revenge.
Lightbringer is the first installment in The Guardians Duology, a young adult portal fantasy series.