If I'm reading the lyric correctly, she already has been hanged!
It tells how Miss Otis "strayed" down Lovers' Lane and shot her lover, "who had led her so far astray". In the last verse, she is dragged (in the past tense) from the jail by a mob, and strung up on an old willow tree. Then "the moment before she died, she lifted up her lovely head and cried, Madam ... Miss Otis regrets she's unable to lunch today."
Wikipedia relates a story from a biography of Cole Porter, by Charles Schwartz, telling how Porter wrote the song as a parody of "a cowboy's lament" that he heard on the radio.
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