Inca Mummy Girl deftly uses the Buffy setting to breath fresh life into a very tired stock theme.
This episode is a good example of how throwing a disruptive element into the mix can generate some friction between the regular characters without doing any long-term damage.
In this case Ampata's arrival causes each of the main characters to reassess their relationships with each other (particularly the tentative one between Willow and Xander).
Matt Keine and Joe Reinkemeyer's witty script contains a lot of sharp dialogue which acknowledges that the audience is usually a couple of steps ahead of Buffy and the gang.