Role in the family? Since when staying at home being a housewife is a predetermined role? They were both working, but she had to give up her career to be the housewife that her husband demanded. That's fucked up, completely traditional misogynistic view. Household chores can be shared, and should be shared. There are many husbands that choose to stay at home instead of be the one providing the family too. That is also an option.
FMC clearly knew nothing, because she was young and naive. She thought being a housewife was something admirable because "it pleases her father", while in reality her mother wasn't even happy having to give up her career, hence her telling FMC to actually be yourself. It's kinda sad to actually see it happen when she grew up because she had an amazing career, but chose to give up on it and be a housewife instead. Is she happy now? Maybe yes, since author wrote it that way. But could she have been happy too if she continue her career? Also maybe.
TL;DR: this is an extremely outdated view of how spouses should work in the society. FMC just didn't know better.
Considering this was old Japan there were roles in the family men and women were expected to do. Also did her husband demand that or are you making assumptions because of your bias? As far as I can tell they were following social norms.
Ah yes househusbands and how well do those relationships last and how much of those are there? Not very long and very few are actually successful. But sure that was an option even tho it definitely might've destroyed the relationship given the heroine's mother probably wanted her husband to work as well.
The heroine is happy not just because the "author wrote it that way" it's because that was her original dream. Because of her mom's terrible advice she thought she had to work when in reality she just wanted to be a housewife.
Ah yes a young girl gets a dream because she saw how well the family structure in their home worked and wanted to replicate that for herself later in their live and she's just "young and naive." You need to curb that bias of yours. Thinking she would be happy if she continued working? Hard doubt and you wanna know why? Because she could've kept working while she was married and she didn't.
Because she wanted to be a housewife. She chose to give up her career of her own free volition because it's what she originally wanted. Not because the author "wrote it that way."
TL;DR: You are completely ignoring what the heroine wanted just to whine about "outdated social norms" and be completely wrong in your analysis of the character. Heroine knew what she wanted from a young age and was sabotaged by her mother.