Aranwen is aware of Kithran's past, as we did establish. In a sense it is something of a wish fulfillment on her part, and Aranwen knows it. Both a desire to make right the wrong caused by another Syl woman, and a desire for family. It's one of those things she'd never admit, because she knows the reality is that is not the case.
A personal perspective, a fantasy held in the mind of the individual that influences their actions and feelings.