Unprotected sex 5 to 6 days prior to period due date is EXTREMELY SAFE if her previous cycle was regular. In case of irregular cycle, it is quite difficult to calculate fertile days and withdrawal method has high failure rate (15 to 27%).
I suggest her to undergo one home pregnancy
test 2 weeks after last sexual encounter to rule out pregnancy. On negative test, progesterone
pill can be given to induce period.
On positive test, medical abortion
can be done under guidance of gynecologist.