The Gemarah in Pesachim 108 A states:
A woman in front of her husband need not recline, if she is esteemed she must recline.
אשה אצל בעלה - לא בעיא אינה צריכה הסיבה, ואם אשה חשובה היא - צריכה הסיבה.
The gemerah states that a woman does not need to recline while eating (hasavah) during the seder, if she is in front of her husband (unless she is an esteemed woman). Why not? Rashbam gives two possible explanations:
A. Because a women is subjecated to her husband ( the hebrew is hard to translate כפופה לו).
B. In the name of Rav Achai Gaon: Because it isn't the women's custom to lean (when pouring wine).
From Rashbam's first explanation it can be understood that a women needs not lean during the seder, because she isn't really free - her husband's fear is upon her (אימת בעלה שכפופה לו). So are women free?
Ashkenazic hallacha did a double step. The Tosfot (As mentioned in the Meiri on the daf - though not in the tosfot we have today) state that today all women are considered important. Ergo they all must Lean. This is somewhat surprising since the Rashbam lived during the same period and geographic location as the Tosfot. The opinion of the Tosfot is accepted by the Rama in the Shulchan Aruch, but it comes with a catch. The Rama states that in his day women do not lean - because they go by the opinion of the Rab"ya (ראבי"ה) that leaning on Pesach is no longer a mitzvah since people no longer lean while eating.
Sepharadic Halacha also did a surprising twist. Originally the Shulchan Aruch (אורח-חיים, תע"ב, ד) copies the gemarah, and paskens that women need not lean unless they are important. This is despite the fact that Rav Karo mentioned the opinon of the Tosfot in his commentary on the Tur ( ס' תעב ד"ה אשה חשובה). However later Sepharadic poskim accepted the Tosefot (who are Ashkenzaim!), and paskened that all women are now considered important, and hence must lean. ( מקור חיים , ח"ד עמ'95 as well as Rav Ovadia - though he brings a different reason).
The bottom line is that all denominations accept today the opinion that all women are considered "Important". What else is interesting is that if we accept the Rashbam's interprentation of why a woman must not lean (and this is the dominant explanation) then this is a clear case of a halacha changing due to the changing social norms.
Hat tip: Ya'acov Gertner article available here - though he interpreted the opinion of the Rashbam differently.