The Tullivers really are a match made in heaven: they are both constatly confused by the world around them. Mrs. Tulliver is definitely not the sharpest knife in the drawer. She’s downright dim-witted at times, and often hilariously so.
For example, check out this exchange: Mr. Tulliver exaggerates how picky his wife is, jokingly telling her, "You’d want me not to hire a good waggoner, ‘cause he’d got a mole on his face." But Mrs. Tulliver takes him literally: "'Dear heart!' said Mrs. Tulliver, in mild surprise, 'when did I iver make objections to a man, because he’d got a mole on his face?'" After talking of the actual "waggoner" the family had, Mrs. Tulliver finally wraps up:
"He might have a mole somewhere out o’ sight, but how was I to know that, Mr. Tulliver?"
"No, no, Bessy; I didn’t mean justly the mole; I meant it to stand for summat else; but niver mind – it’s puzzling work, talking is." (1.2.6-8)
This confusion spills over into Mrs. Tulliver’s other personal interactions too. She never seems to get a good handle on how to deal with people, or her own family at least. Maggie confuses and frustrates her, and her husband’s actions in the lawsuit eventually result in difficulties that are almost too much for her to comprehend. The thing Mrs. Tulliver really seems to "get" are in fact, things. She is a superficial woman who places a huge emphasis on her material belongings. And she proves lost without them:
The objects among which her mind had moved complacently were all gone; all the little hopes, and schemes, and speculations, all the pleasant little cares about her treasures which had made this world quite comprehensible to her for a quarter of a century [...] had suddenly been snatched away from her, and she remained bewildered in this empty life. (4.2.2)
In fact, this loss of her belongings leads Mrs. Tulliver on a slow and steady decline. By the novel’s end she is practically a shadow of her former self – she exists simply as Maggie’s and Tom’s mother and as Lucy’s aunt/housekeeper. Mrs. Tulliver’s fate is a truly tragic one, and it is one that receives a notable lack of attention – though it may be that this lack of attention is a narrative device to reinforce Mrs. Tulliver’s decline as an individual.
The bankruptcy is the great crisis of Mrs. Tulliver’s life. When the family goes bankrupt, Mrs. Tulliver treats it like a sort of life-and-death garage sale – she desperately tries to pawn off her belongings onto her siblings, essentially begging them to help her keep her identity intact. Mrs. Tulliver’s whole sense of self is rooted in her belongings. These household things represent home and family and a predictable world for Mrs. Tulliver. Without these things, she is "bewildered."
And Mrs. Tulliver’s bewilderment is most strongly felt in the presence of others. As noted, the woman has serious problems interacting with her family members. We interestingly almost never see the extended Dodson clan interact with anyone except family members. And the few scenes we do get really stand out. Aunt Glegg getting conned by Bob Jakin places her in a whole new light, for instance. And Mrs. Tulliver’s major, out-the-box scene is her hopelessly misguided confrontation with Mr. Wakem. Poor Mrs. Tulliver unintentionally encourages Wakem to buy the mill, an act that eventually leads to Mr. Tulliver’s death. This isn’t to say that Mrs. Tulliver destroyed her entire family, or anything that dramatic. It does demonstrate that the world is never predictable, though, and this is a lesson that Mrs. Tulliver struggles to grasp.