I am willing to bet that Ria like similar based fantasy stories is the cliché princess, at most a high noble of some sort. It's so obvious from her entire attitude; brazen speech, low sense of danger and ornament gear = Noble.
I assume she was possibly abducted during transit in company of her compatriots, or the other cliché angle is a disaster befell them, hence how she probably ended up alone/memory loss then kidnapped, as I don't see her being the running away from home type.