She runs straight out of the party, in her stupid party shoes that make her feet hurt and her stupid party dress that makes her look like someone who deserved what she got. She runs with tear-blinded eyes, into the street and away, and no one runs after her. She runs, and keeps running.
She doesn't know where she's going. She doesn't care where she's going. She doesn't have anywhere to go.
When she sees the lake in front of her, it isn't that she decides to jump. It's more like she doesn't decide not to.