Her last appearance was in Alone Again, Natura-Diddily. The one where she was killed by a t-shirt cannon that was meant to fire at Homer but hit her instead after he bent down to pick something up.
In the episode where Bart broke his leg he uses a telescope and he sees Ned and it sounds like somebody's screaming and then he sees Ned fill in a grave and Ned says he's a "dang-diddly" murderer. There's also an episode where Maude gets hit by a t-shirt cannon and dies. She gets knocked over the edge of the stadium. So there are two episodes.
