Isekai kara Seijo o Yobeto Mucha Furi Sareta Shinkan wa, Ko Spa no Tsugou de Seijo ni Naru Series

A Fake Isekai, But A Real Saint?!
“Summon a saint from another world.” Thanks to their daydreaming king’s unreasonable demand, the members of the clergy, including Fiona, are at their wit’s end. The country has enjoyed a long stretch of peace in recent years, so it would be a waste of the national budget to spend the astronomical amount required to summon a saint. While turning the problem over in her mind, she realizes something. The saint summoned in the neighboring nation has black hair. And Fiona herself, who for whatever reason finds herself the object of the handsome prince’s affections, also has black hair, an unusual color in their country. The time has finally arrived for her tresses to prove useful.
“Let’s pretend I’m the saint.” The kingdom’s finances and working conditions for her fellow clergymen must be protected at all costs. So in collusion with the prince and the head priest, Fiona resolves to deceive the king by taking on the guise of a cost-effective saint! While she runs hither and fro alongside the overprotective prince with a borderline unhealthy obsession with her hair, where will Fiona’s life as a fake (?) saint lead her?!

[From Cross Infinite World]