she is most likely having a condition that is called as costochondritis which is an inflammation of the cartilage that connects the ribs to the breast bone...
the symptoms of this condition include:
sharp pain which may be increased by deep breathing and coughing as well...
this condition is benign (harmless) and generally goes away on its own and all that is usually required is pain killers in the form of advil or aleve
the exact cause of this condition is not known..
you can read more about this condition, the causes, symptoms, treatment from the link below:
http://www.mayoclinic.com/health/costochondritis/DS00626/DSECTION=1
please let me know if you need more input
regards
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