(Not a health professional.) That is called a chest retraction (at least if her chest is pulling in between her ribs), and it's a sign that she's working really hard to breathe. Medical professionals do seem to find it a bit worrying, just because little kids can go from "hard to breathe" to "not breathing well enough to get enough oxygen" fairly fast. I'd take a kid to a doctor with chest retractions. If you're in the Australian Capital Territory, New South Wales, the Northern Territory, Tasmania, South Australia or Western Australia you could ring healthdirect on 1800 022 222, in Queensland 13 HEALTH (13 43 25 84) and they can advise you how soon you need to see a doctor.