Must Remember by Colleen S. Myers

Like Roswell meets Lost in Space

Nineteen-year-old Elizabeth ‘Beta’ Camden is a survivor. When the E’mani—those pale alien freaks—destroy Earth with a plague of madness and scoop up the remains, Beta is one of the ‘lucky’ ones. For years, she endures their tortures, experiments and games. Then one day, she manages to escape their ship with her life, and no memory of her time with them.
Stranded on their world, Beta wanders the mountains, looking for a way home. She stumbles onto the Fost—the E’mani’s ancient enemy. Their war with the Imani is old and rooted in magic that the Fost once had and the Imani crave. Magic Beta soon discovers she’s developing along with strange tattoos and disturbing glimpses of her past. The Fost take her in and train her in their ways. As she spends more time with them, she falls in love with their culture and with Marin—he of the hot hands and slit eyes.

But the E’mani took her for a reason and they want her back—dead or alive. If Beta doesn’t remember that reason soon, they’re all going to die.