Idaia thought the dreams were real when she was little.

This does not significantly move her when she is nine, ten, eleven. When she was little little, like four or five, she believed that honey was made from melted gold and your stomach was literally located in your abdomen. Dreaming--fantasizing--that you're the Grieving Prince's lost wife reborn is--well, it's not exactly normal to have recurring, consistent internally and between them, literal dreams about it, but it's a reasonably normal fancy. There's self-insert RPF of it on the 'net. She looks it up, every so often, to see if it's gotten any better. It hasn't.

(She reminds herself that the character who exists in her head isn't any more based in reality than what any of these other girls think the Grieving Prince is like. She reminds herself that if she ever actually met him she would be inevitably disappointed when he failed to be the person she was imagining. But the discrepancy in imagining still makes those other girls' stories unappealing to her.)

(It's weird that Imliss also has the dreams, and that the two sets are consistent with each other, but obviously it's just that Imliss has heard enough detail about Idaia's dreams to have started regurgitating them.)

She makes peace with it. The dreams aren't all pleasant--some of them are downright traumatizing--but hey, the Prince's wife had to die somehow. She falls more and more in love with her imaginary Tyelcormo, and sighs and resigns herself to singleness forever because real boys can't compare to fictional ones, and if she had the cultural context to do so she would call herself a Pygmalion longing to make her Galatea live but she does not so she does not.

And then--

One day--

Wholly by accident--

She does the magic she can do in her dreams