The Valkyrie's Shadow(Helheim Prophecy‪)‬

Being both a valkyrie and a princess isn’t turning out quite the way Sigrid imagined. The other valkyries still treat her like a stable hand. Her relationship with Mariam is less “long-distance” and more “worlds apart.” And lately, she’s been wondering if Sleipnir, her new horse, isn’t making her a little bit … well, evil.
But Sigrid’s first official valkyrie mission sends ripples through the Nine Worlds.
She’s attracted the wrath of not only the Night Elves but their sinister king, who wants nothing more than to bring darkness down on everyone. Worse yet, Loki might just be interfering with the balance of light and dark …
When war threatens the shores of Vanaheim and her friends are in danger of being exiled, Sigrid makes a deal with the new queen. She will ride Sleipnir against their enemies and use his might to defeat them, even as he pulls her closer to that line between good and evil.
What she becomes will either save everyone … or unleash disaster upon them all.