Kendra / am I missing something?

In “What’s My Line? Part 2” Kendra and Buffy are talking in Giles’ office and Kendra tells Buffy that her parents sent her away to her watcher when she was very young because they believed it was the ‘right thing to do’ — is it just me or does this not add up at all and is a bit of a plot hole as Kendra wouldn’t have been called as a Slayer until Buffy died, when Kendra would have been around 15/16 - only a year before she visited Sunnydale in this episode.

Am I just missing something? Because it seems like such a large oversight!!