|Robyn Jacobs reads her sister's diary and tells all of her close friends about it. When Melanie finds out, she feels betrayed and tries to get even.
Robyn Jacobs was in the series for about 3 or 4 years. There was no apperance or mentioning that she had a sister now her sister just suddenly appears. It seems kind of strange to me for a major child charactor to be in that long with no mention of a sibling.
In this episode Eugene states he doesn't keep a diary but simply memorizes everything. However, in "...It Ended with a Handshake," it's made clear Eugene keeps a diary on his computer, and in "The Time has Come" he inputs into the Imagination Station his diary of his complete life in Odyssey and sees parts of his life before and around this episode, when he searches his life using the Imagination Station.