Koushaku-sama wa Watashi wo Moteasobu no ga Osuki

Ravelli Attilie was sold as a maid at a young age and grew up without an education. She used her natural talent for writing to become known among commoners as "Madame Rosa," a love letter writer. But one day, an anonymous nobleman asked her to write a love letter for his younger brother, Cedric. Wanting to
earn money and leave the mansion where she worked as soon as possible, Ravelli put all her effort into writing love letters to seduce Cedric, but after sending out a few letters, she received a reply with her real name written on it...!

(Source: Amazon, translated)