Migawari de Endan ni Sanka Shita Gumai no Watashi, Ringoku no Ouji-sama ni Misomeraremashita

There is only one saint in a generation. The twins Hestia and Astrea overturned this rule. However, the only one who can make miracles is Hestia, the older sister. Astrea is looked down upon as incompetent, and is forced to take part in marriage instead of her arrogant sibling; but by chance she meets Silvert, the second prince of the neighboring country, and she ends up getting engaged!? A Cinderella love story between an incompetent saint who dreams of average happiness and a prince who sees through to the truth!

(Source: M Novels f, translated)