Jack's mom embodies the spirit and values of the original Norvelt: she is community-focused and is always ready to lend a helping hand to anyone who needs it. She grew up in Norvelt, and "[s]he knew and loved everyone in our little town and they loved her too" (4.44).
No matter what you think of Mrs. Gantos's communitarian ideals, you have to admit that she's one nice lady, selflessly donating her time and labor for helping the poor and elderly in the town.
That's one reason she's so mad when Jack mows down her cornfield: she was growing that corn to sell in order to buy food for making charity dinners for the sick and elderly (4.30-32). She comes down pretty hard on Jack for this, and we can see how important taking care of the less fortunate is to her: "You took food away from hungry people. From poor people. Nothing can be lower and more cruel than that" (5.63).
But there's a problem with this mode of thinking. Jack's mom is sort of living in the past—like, the way past—when it comes to how things work financially. She tries to buy things by bartering (exchanging one item for another of similar value). For example, she tries to buy Jack's nose surgery with some home-canned fruit, and offers to exchange Jack's labor for the services of the farrier.
To her, a trip to the doctor is similar to borrowing a cup of sugar (7.9). Problem is? These trades are worthless, because everyone wants cold, hard cash—and they want it now.
Jack's mom is a strong female character, just like Miss Volker. (Huh. Speaking of, what is it with all the bad dudes in this book?) She's the primary adult figure in the household, since Jack's Dad is so childish, and she pretty much "wears the pants in [the] family" (13.9). Even Jack's dad is afraid of getting in trouble her, going so far as to hide out in Jack's room and the garage to avoid being scolded by his wife. Actually, he goes even further, getting out of town when she's extra mad (6.1).
She can also hold a grudge and hang onto anger: "It was as if she could preserve her anger and store it in a glass jar next to the hot horseradish and yellow beans and corn chowchow she kept in the dank basement pantry. And when she needed some anger she could just go into the basement and open a jar and get worked up all over again" (6.1).
With such a strong personality for a mom, is it any wonder that Jack is a little, well, weak? Maybe not. But it also makes sense that he ends up finding the same kind of strength—and even anger—by the end of the novel.