What is the meaning of 奴 this poem from 红楼梦？
It is kind of 谦称 of a woman in ancient China, there are others of course

妾 or 妾身 or 奴婢 for you being the wife
奴 or 奴家 for you being the wife or general cases
小女子 for general cases
老身 for older ladies

And for men of course, their 谦称 could be

小人 for you being the servant
鄙人 for general but unofficial use
在下 for you being in a relatively lower social hierarchy
晚生 if you are younger to your friend
不才 for proposing suggestions
不肖 for referring yourself with respect to your older relatives
愚弟 or 愚兄 for closer relationship