I don't know it but if it's in ancient China and it has some fantasy vibe maybe you can look under the wuxia tag or try looking at the the historical-romance-martial arts one. Maybe you'll find it if you know how the characters look
Ah, the site is novel updates
i don't know if it's http://www.mangago.zone/read-manga/gu_fang_bu_zi_shang/
but the MC here became a maid, there is a zither (she's good at it), the ML is a general and it's historical with a (completed) Chinese Novel that you can read from NovelUpdates (this is my very first chinese novel and i absolutely love it!)... the manhua has stopped updating so i resorted in reading it's chinese novel. there is drama for it too (The General and I, i think is the title) but i haven't watch it.
unfortunately, from my memory, this really is the closest that i can remember though the rich young girl has really no brother. the maid has a master (before) that she looks up to
sorry just following
I'm not sure if this site will be much help but here it goes.
I'm looking for a novel about a girl who grows up as a maid to a young girl the young maid eventually grows up as a close sister to the girl. The girls older brother falls in love with the young maid. Its in ancient times with zithers and martial arts as well as princes and such. Idk help if you can