In The Effect of Gamma Rays on Man-in-the-Moon Marigolds the character of Beatrice is meant to be an antagonist. For this reason, Paul Zindel accentuates her negative traits by intensifying their effects on the family: gravity, chaos, discord, and cruelty. The dysfunctional nature of Beatrice's traits is most evident in the way that Beatrice treats her daughters, as well as everybody else around her. In the end, it is not known to the audience whether Beatrice, as an antagonist, gets her just deserts, or if she ends up dominating her entire household.
The first evidence comes from the stage directions. The scene shows a myriad of scattered items which "respectable people usually hide in closets" such as empty bottles, trash, magazines, laundry, etc. As a head of her household, what does this say about Beatrice? It clearly shows the chaotic state of the house which she runs.
Secondly, Beatrice embodies bad parenting and bad manners in the way that she hypocritically and sarcastically speaks over the phone with none other than Mr. Goodman, her daughter's teacher. The fact that she scornfully downplays every compliment that Mr. Goodman bestows upon Tillie shows undue resentment and an immaturity of character on Beatrice's part. Moreover, Beatrice directly abuses Tillie and Ruth verbally, and neglects Tillie's rights for an education by making her stay home to do household chores.
Then, there is the drinking. The play clearly shows that Beatrice has a marked alcohol problem that is triggered by stress, and which itself triggers all of the wrath and pent-up life frustrations to come out and lash out against her daughters. Beatrice holds an extreme amount of negative and destructive energy; she causes a chain of events which often start with Ruth stressing out to the point of getting a seizure. All goes haywire from there on, and the action of the play basically falls into a black hole.
Yet, out of all the negative features in Beatrice THE most salient characteristic is her egotism. As a parent, she cares little for the emotional needs of her children and, instead, indulges in pleasing her own; she switches from hot, to cold, to erratic, within seconds. This, combined with the evident self-loathing that she feels, turns Beatrice into a time-bomb for her children. Instead of resolving to act maturely, Beatrice acts childishly: she does not attend her daughter's presentation, she badmouths and insults the teachers who entreat her to see Tillie's science presentation and, to top it all, she kills Tillie's pet the VERY night of the science fair just to spite and ruin Tillie's night. It is as if to say, "if my life is ruined, I will ruin yours, as well".
Again, it is not clear where her actions lead at the very end of the play; she simply ends what could have been Tillie's most magical night by causing a massive seizure in Ruth, and by killing from its root the joy of Tillie's first place prize. That is classical egotistical and histrionic behavior, and the most salient of Beatrice's traits.