I want to first start by saying you reeeeeally helped me in a previous question I asked (moving the fuck on).
Anyway, I have a friend, who’s family has always kind of treated her like a step child. Her sis is the princess (mind you a princess who said she was going out of state for one week to vacation and ended up staying there to live with a boy, boy got her pregnant, some months later move back here to CA on mommy/daddy’s dime with baby and bf in tow). Her bro is barely around (always at his gf’s). My friend just got a job in her career which she loves but still lives at home to save money. I’m afraid for her sanity that she needs to move out and get her own place, at least a little apartment because her mother is ALL in her business (i.e. looks through her bills and statements to see how much money she has, always asks her who texted/called her, where’s she’s going, who is she talking to on FB, etc. It’s ridiculous. Even more ridiculous is her sis, who lives few doors away (with bf and baby) in same apt building, who thinks its ok to steal my friends clothes out of her closet (even ones with new tags) and get mad at my friend when she asks for them back. I feel bad for her, and I don’t know how else to tell her that she should move out soon for her own sanity? Mind you, she isn’t a kid/teen (she’s 26). And with her job now, I’m sure can afford at the least a studio in our area.
Like you said, she’s not a kid. If she’s not in danger, it’s best not to interfere with family business.
Privacy and dignity are the cost of living under your parents’ roof in your twenties. She may be saving money, but nothing is free.
As long as your friend considers her privacy and dignity to be worth less than rent on a studio apartment, there’s nothing you can really do.