This is a theme that might not pop out on a first reading of "The Laboratory," but when you look back, you start to see it everywhere. Men are basically background characters in this poem—we don't hear from them or really learn anything about them. The speaker is a woman, her intended victim is a woman, and all of her anger and jealousy seems to be pointed at other women. On top of that, she talks a lot about the little details of being a woman in her time and place—flirting, dancing, seduction, jewelry, accessories, and so on. Even the act of poisoning itself is stereotypically seen as a womanly act (as opposed to, you know, sawing off someone's head with a broad sword).
"Chill out ladies," Browning seems to say. The poem depicts female competition as the root of evil plans, and leaves men out of the picture entirely.
The poem shows us the speaker's power and intelligence, but also her helplessness. She is forced to bribe men and attack other women in order to get her way. Sad to the max.