Original: Though initially planned as a five episode role , the character became so popular that she stayed on for the entirety of the third season and returned for a two-part appearance in season four , after which the remainder of her original story arc was played out as part of the first season of the Buffy spin-off series Angel .
Simplified: She stayed on for the rest of the third season and returned for a two-part appearance in season four . She was then used as part of the first season of the Buffy spinoff series Angel .