Her guy friend tried to force himself on her, she ditched him, got with her girl, who apparently had an older brother whom the girl had known for a long time... he made some flirty comments about her being all grown up, they looked at each other, she sang to him, they all went and saw some fireworks, then she crept into the living room where he hit it that night.

I considered all of what you're talking about. And I'm all for filling in the blanks and all, but not only is what we saw not very much to draw such conclusions from, but this read on it makes the tone of this segment jarringly out-of-step and darker than the lighthearted tone of the rest of the film...
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