I think what you are doing is correct a painkiller and cold fomentation would prevent hematoma
formation.What you need to observe in the next 24hrs is any vomiting
,change in behaviour or abnormal movements in the form of fits.If there is anything positive then meet her pediatrician
immediately If nothing like this happens then maybe it might have been an external injury
.However i guess its better you could fix up an appointment with your pediatrician for assessing her the next morning.