If jealousy is what motivates the speaker in "The Laboratory," revenge is what she's after. Big time. This whole poem is about plotting revenge and taking steps to get it. She doesn't just want to bump off her rival, she wants everyone involved to know that she's not someone to mess with. She wants everyone to see the kind of painful, terrible death she can inflict if anyone crosses her. That's hardcore. Again, Browning is painting a grim portrait of just how terrible the effects of romantic betrayal can be, and how low the human imagination can sink as a result. Real low. Think ocean floor, then start digging.
Silver lining alert: "The Laboratory" is a celebration of the grisly fun of revenge. Even though we know we're supposed to be horrified, it's hard not to root for this lady who just can't take it any more.
Dark cloud warning: This poem is a study of the terrible consequences of revenge. It digs into the twisted psychology of a killer, and forces us to think about the line between righteous anger and insanity.