Little of her backstory was revealed in the television series, other than that her family was obviously well off (Her house had wings, her summer house only had one) and she had a half-sister. She butted heads with Buffy quite often and seemed to look up to Faith. From the first episode she was introduced in, she made it her goal to get Willow. Whatever her original intentions were, it quickly became a real relationship.
Early on in Season 8
(the comic continuation of the show) she makes a few cameos, first as the girlfriend to Willow, with great chemistry and cute banter, then later in Japan to evaluate Satsu
's performance as a field leader (and gay-type mentor). They bond and Kennedy takes it upon herself to help Satsu get over Buffy (in a totally platonic way; she's dating Willow after all.) It is insinuated early on that Kennedy died briefly at some point, by Willow in a conversation with Buffy, however no details of what happened have been given.