What does it mean when a girl sighs or breathes deeply?

So there's this girl and I think she likes me. Among the usual things (eye contact, glancing, shy when I talk to her .etc) she sometimes sighs or breathes deeply when she passes by me or is in my vicinity. She is also clumsy .eg. dropping her books very often. Is the sighing a way of looking for attention or is it just her nerves? Do many girls do this?
What does it mean when a girl sighs or breathes deeply?
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