Here's a breakdown:
* Book 19: Melantho, along with other maids, insults Penelope and mocks her loyalty to Odysseus. She also actively encourages the suitors to stay and pursue Penelope.
* Book 20: Melantho continues to disrespect Penelope, even after Odysseus's return is revealed. She helps the suitors plan their attack on Odysseus and tries to warn them of his intentions.
The specific instances of betrayal are woven throughout these books, not confined to a single page.
It's worth noting that the *Odyssey* is a complex poem, and its narrative unfolds over time. While Melantho's betrayal is a significant event, it's a gradual process of disrespect and undermining of Penelope's authority.