Soul of Light and Thunder (Soul Erosion #1) by Arianne Nicks:
 
A contemporary fantasy story about power, magic, and love.

Sophie’s mission is to hold on to a beloved heirloom. For her, it’s just a simple mirror. But for others, it’s a key to tremendous power.

When a whole new world full of magic is revealed, Sophie learns that her amulet can bring peace or chaos to it. She thought college was going to be the most exciting time of her life, yet the lurking danger and an all-consuming love make studying seem insignificant.

Will she risk the collapse of a world she barely knows to save her life, or hold on to the mirror to keep her promise?