"I am Poyser, hear me roar!" Okay, okay, so maybe a contented farmer's wife like Mrs. Poyser isn't a raging proto-feminist. She's more concerned with keeping a clean house and running an efficient dairy than with overturning the local patriarchy.
And she has to be tough customer to get some of this done. Don't cry for her; cry for the hired help, because Mrs. Poyser's—
[…] tongue was not less keen than her eye, and, whenever a damsel came within earshot, seemed likely to take up an unfinished lecture. (6.8)
But when the local patriarchy comes knocking (that's Old Squire Donnithorne) Mrs. Poyser can hold her own. Even though there's nothing "elderly or shrewish" about her, she stands her ground when upper-crust machinations threaten her hard-won prosperity (6.8). In Poyser-speak:
"I'll not make a martyr o' myself, and wear myself to skin and bone, and worret myself as if I was a churn wi' butter a-coming in't, for no landlord in England." (32.32)
In truth, Mrs. Poyser is a creature of a different era—and not just because "butter-churners" are a dying breed. Nowadays, we've got plenty examples of how incompatible family life and self-assertion are. Mrs. Poyser is the opposite, a self-assertive homebody. And it's a virtuous circle, too. Her assertive ways keep the household running smooth; and her household gives her something worth defending.
Just when you start thinking that Mrs. Poyser is good mainly for a rant or a laugh, Eliot reveals a whole new side to the ol' gal. Just look what happens when Hetty—Mrs. Poyser's own protégé—runs afoul of the law. The normally "mild people" who make up the rest of the Poyser household are all coldness and condemnation (40.17). But Mrs. Poyser tries to reassure them, since "there's One above" to watch over the family (40.23).
Not expecting that, were you? That's the point. Adam Bede depicts the "deep pathos" and "sublime mysteries" of human nature (17.14). No, not mysteries like how David Blaine does his magic tricks; mysteries like the soft side that even the thorniest person can show. Like real examples of human nature, characters like Mrs. Poyser have the power to surprise us, and inspire us. Adam Bede himself sums up her best:
"If her tongue's keen, her heart's tender: I've seen that in times o' trouble. She's one o' those women as are better than their word." (53.61)