I think it was explained(idk if u made this comment before or after the recent chapters came out where it explained this but....) that it was voluntary(at least the dress part) cuz FL wants to dress her bestie up prettily. Kinda like that feeling of wanting the best for someone? Or the pride of making them look good/feel good? I think the attic/seperate room was requested by FL so she doesnt "hurt anyone" or so it says im guessing on her full moon days. Idk why it isnt a better room honestly though, that doesnt really add up. Plus maybe also the fact she says "she hates being noticed by people" so that mightve factored into her wanting to live more lowkey/not as a rich lady. The hand me downs might be her more like she doesnt really see the point in dressing up + being lowkey and not wanting the best. I think her siater wasnt rlly jealous of her but rather like being protective of her sister
If the sister is such a good person, why is she letting her step-sister (FL) work as a personal servant? This girl is the owner of a great mansion but lets our good sis sleep in the attic/ store room?? she only wears hand-me-downs. really?? She cannot hide her anger and jealousy about the Duke (Yannic) wanting her sister. naaaaahhh!! she's not a good person.