Shirley is a portrait built from almost nothing: a head of hair, an early start, and a small routine. The speaker never says who she is or how they know her, and that restraint is part of the effect. We get her the way we might get a neighbor or relative, through the things she does again and again.
The first two lines are clipped and rhyme neatly, "curly" with "early," which gives her a brisk, almost nursery-rhyme quality. Then the last line slows down. Cigarette, whiskey, sleep: the commas string together a short ritual that seems to end the day, or maybe begin it, since she's up early and going back to bed. The poem suggests someone whose days have a worn, repetitive shape.
The mood is quiet and a little weary. The speaker doesn't judge her, though. There's a plain, observant tenderness in noticing someone this closely, and in letting the details stand without explanation.