On the face of it, there don't appear to be too many similarities between Sal's mother and Mrs. Winterbottom. Whereas Sal's mother is very much one of life's free-spirits Mrs. Winterbottom is so much more staid and conservative, someone whose whole life revolves around being a housewife and mother.
Nevertheless, both women share a common bond in that they find it increasingly difficult over time to reconcile the demanding roles of wife and mother. Although home is Mrs. Winterbottom's natural habitat, her comfort zone, if you like, she begins to feel unappreciated by her family, who take her for granted.
As a result, Mrs. Winterbottom starts to question whether the identity that she's adopted all these years, that of homemaker, is an accurate reflection of who and what she really is. So she makes the fateful decision to leave home and head out into the big wide world in the hope of finding herself.
As for Sal's mother domestic life is also making her deeply unhappy. On top of everything else, she's suffered a miscarriage and a hysterectomy, which combine to make her clinically depressed. In order to restore her rapidly failing mental health Sal's mother goes to visit a cousin in Idaho in the hopes of reconnecting with her true self, with the identity she once had before she got married.