We learn a ton about the speaker of this poem. In fact, she spends most of the poem describing her feelings, desires, plans, fantasies, etc. We learn that she's wealthy enough to have jewels, and that she's used to hanging out at the royal court. More importantly, we learn that she's just been dumped for another woman, and that she's planning to get revenge (not on the jerk who left her, of course, but on his new girlfriend). But as we learn about her plans to get even, we also learn that she's really excited about killing people. She turns out to be bloodthirsty, sadistic, crazy-jealous, and obsessed with death. She's also willing to use anything—her body, her money, her brains—to get what she wants.
But maybe there's a bright side to that determination. Over the course of the poem, the speaker shows us that she's curious, strong-willed, and imaginative, too. Okay, maybe she's also crazy, but that's all relative, right? After all, she is a victim of betrayal. Anyone who has been in her shoes might be sympathetic—not murderous per se, but sympathetic. So, is Browning asking us to see his speaker as someone wholly evil? Or are there some positive qualities to her, as you see it?