I would have loved to have Jenny stay for the whole series, that would have been nice Giles to have another adult to interact with.
Do you guys remember Nancy from Beneath You 7.02? I thought for sure they were going to make her a regular! The way she kept tagging along with Xander, Buffy, and Spike to the Bronze and everything, I thought they were gonna start something between her and Xander. Honestly, I think that would have been kind of neat! Have someone they help out become a member of the Scooby Squad! She seemed nice and had a nice wit about her! (She said something to the effect of, "Have any of you not slept together?" to which Xander and Spike look at each in the most hilarious way!)
