Why is she so eager to give back the headband? That is not how people and headbands usually work --
Oh right. Mariona hates hates hates Eagle's Splendour, which is why Esta prepares it every time he can spare a 3rd-circle before meeting her. And of course one doesn't cast Owl's Wisdom on a 2nd-circle cleric, and even 3rd-circles are mildly warned against that before they get to 4th (though if you need the +2 to WIS-based checks, you need it, so it's not a strong warning).
"If 'growing more ambition' is what you meant by {Protagonist Growth Arc} you could have just said that, young lady. I am thoroughly familiar with Mariona's difficulties in this area and their lack of response to either positive or negative incentives, though I hadn't thought them so extreme as to interest an Outer God in the challenge. One sign of 'ambition', by the way, will be when you are reluctant rather than eager to remove a headband that makes you more than you were."
"But I will be glad enough to have it back." Esta holds out his hand, deciding to forbear to mention how much added difficulty there would be in removing the headband if Merrin did not voluntarily take it off.