I think she's just an earth mage who wrong place at the right time to encounter Sammael, and probably wasn't too happy about her prospects in life so going across the mountains with a massive himbo to convert to Halloween Feminism wasn't the worst option. She still thinks that when she gets there, she'll be obligated to marry Sammael, but he assures her that when she passes her initiation, she'll be free to marry whoever she wants and that he's not great husband material anyway.