Did she wind herself? If she is breathing ok and is behaving otherwise normally, I wouldn't worry too much. How long ago did it happen? Brusing to the chestwall is jolly sore, but might not be immediately apparent. Give her some Calpol. Unless she fell off a great height or onto a sharp ledge she is very unlikely to have broken anything - 7 year old ribs are very flexible .
If it hurts when she coughs (so much that she actually cries) she may have broken them, but there's very little that can be done. So long as she is breathing okay, just treat with painkillers and (limited) sympathy