You shouldn't ruin your family's Christmas.
Selena is at her parents' for Christmas, and so is her sister, whom she not seen in a long time because of a conflict between them.
Selena wants to tell her sister how frustrated she is with her.
Selena waits after lunch and goes for a walk with her sister during which she tells her about her frustrations.
Selena starts telling her sister about her frustrations in the middle of Christmas lunch, with the whole family watching.
The family's Christmas lunch goes well and people are in a good mood.
The family's Christmas lunch is ruined and everyone is disappointed.