Attack of the Killer App - S6-E3
Other mistake: As the Antarians are stripping Bender, the hinges for his door are shown on the left. However, the hinges should be on the right.
Lrrreconcilable Ndndifferences - S6-E11
Other mistake: When Lrrr is looking at his reflection in the clothing store, the necklace he's wearing is seen as it appears normally, not reversed as a mirror image should be.
Answer: You are thinking about episode 20 of series 2 - "Anthology of Interest I". She technically never kills anyone, but in the episode she ask a "What if machine" (one of the Professor's inventions) what would happen if she was more impulsive. The machine then shows the more impulsive Leela killing off the Professor to get the money from his will and thereafter killing Hermes, Bender, Scruffy, Cubert, Nibler, Amy and Zoidberg to cover it up. Finally she does something really impulsive with Fry.
Andreas[DK]