Hi, Me And My Girlfriend Had An Unprotected Intercourse Earlier.

Hi, me and my girlfriend had an unprotected intercourse earlier. She said shes’s using the calendar method. She had her first day of period last October 25 and today was the 7th day. I dont have enough knowledge abouy the calendar method. Im afraid tha she might got pregnant. Is there any way we can prevent the pregnancy just in case? or is it safe to rely on the calendar method?