Maryoku ga nai Kara to Mendougoto wo Oshitsukerareta Watashi, Tsugi no Shigoto wa Koushaku Fujin rashii desu

Due to her limited magical powers, Algerita, the daughter of a count, is forced by her family to take on the tough job of caring for a dragon. She is then expected to marry an elderly duke, but when his grandson Margus informs her of his passing, she is in danger of losing her job! He then says, "Just marry me," and she ends up becoming his wife!? She thought she was being entrusted with caring for his beloved dragon and that it was just a contract marriage, but he treats her like his real wife...

(Source: KADOKAWA, translated)