Antibiotics rarely have side effects other than basic nausea, diarrhoea etc but it does vary according to kind and there are a couple that rarely have potentially serious side effects. Agree with Gnizmo as to finishing them unless side effects are causing significant problems.
Fracture: as above, weeks rather than days.
Delayed concussion would be odd but still possible. If it's just headaches then that may be due to the cheek injury (referred pain) or another more minor bump that she got that was overlooked due to the cheek. Anything more than MILD headaches and she should get checked out again. There is one condition that can occur days or weeks after a head injury which is very serious which would need to be ruled out BUT it is EXTREMELY unlikely. Good judgement goes a long way.







