Shadow Voyager (Whispers of the Veil #1) by Sharon Garrison:
 
Abigail's secret is her greatest curse. Or so she thinks...

For seventeen years, she has spent her sleeping hours on the outskirts of a menacing realm with red-eyed beasts held at bay by an infinite, impenetrable wall.

A mysterious shift causes Abigail to wander through the wall, and into the Land of the Dead where she is followed home by a hooded, skeletal figure that only she has the ability to see.

Thrust into a reality where monsters and magic abound, she must unravel ancestral secrets, navigate ancient prophecies, and face her greatest fears in order to survive in a world where powerful forces won't rest until she's dead.