At some point or another, every teenager thinks his or her mom is a little nuts. Let's put it this way: Your mom has been nuts, but for your sake, we hope she's never been "drunk while wearing sexy boots as cats crawl all over her" nuts.
There's evidence to suggest that at one point, Beth must have been a functional human being. She makes waffles for her son and husband, prepares a birthday dessert for Doug after the two of them have a fight and throw the cake on the floor, and consoles Karl when his dad gets angry at him during his brief career as a Communist. But then her husband died, and it seems to have been all downhill from there. "By that time, my old Mom was mostly gone, replaced by Flying Saucer Lady, Beth with the Boots, or Neil's Old Lady," Karl says. "Somehow, that party was like the wake for the mother I'd grown up with" (14.1). Yikes.
It's kind of an understatement, really. We here at Shmoop specialize in literature, not psychiatry, so we're not actually going to try to give Beth a formal diagnosis, but it's pretty clear that she indeed "has a lot of problems" (21.30). She's desperate to be young again and has shed her 1950s housewife image for something like a desperate, aging hippie. "Her hair wasn't long yet," Karl describes, "but instead of the ash-blonde pageboy, she now had an untidy mop of hooker-blonde hair; she looked sort of like a dandelion smoking a cigarette" (14.7).
And then, there are the cats. Heavens to Murgatroyd, the cats. Guys, Beth Shoemaker is the original crazy cat lady. Karl buries them in the backyard on a weekly basis and has lost count of how many she actually has. Obviously, Beth is a fictional character, so we can only imagine what this looks like, let alone how it smells. We figure it probably goes something like this.
But, wait. Before we get too hard on Beth for being a neglectful, crazy cat woman who steals her son's hard-earned dough, we should probably look a bit closer. Based on some things she opens up about during her and Karl's waffle fest in part 4, it seems like Beth dove into marriage at a young age, with little concept of who she was outside of her relationship with Doug:
The world played kind of a dirty trick on me. Maybe on every woman my age. When I was ten, the last winter of World War Two, me and all my friends used to say all we really wanted was the five B's, in the right order—bra, boyfriend, bridal show, bungalow, baby. (19.39)
Simply put, Beth set her expectations for life too low and found that being married and having children wasn't all it was cracked up to be, especially when she and her husband both became alcoholics and she later lost him to lung cancer. Really, it's no surprise that Beth went to the dark side and became who she is for most of this book.
Perhaps she's not trying to be malicious toward Karl. Just maybe, she really wants to discover who she is because she never got the chance to as a young woman. Instead, she let other people tell her who to be. "There's so much crap floating around in the world and [Dad] never let her think for herself enough to sort it out," Karl says. "He told her to be a Democrat and a Methodist, so she was" (26.99).
DISCLAIMER: We're certainly not defending stealing from your kid or partying when you have actual responsibilities. But, given what little details she gives about her past, we can kind of see how Beth gets to this.