Do we have to use condoms in the week that my girlfriend stops taking pills?

Your girlfriend is protected against pregnancy during the whole period, also during the pill free period. So there is no need to use condoms. You cannot compare contraceptive pills to taking an aspirin, taking effect right away. The pill influences the whole menstrual cycle. It is important however that your girlfriend does not make her pill free period longer than a week. Because then ovulation may take place, increasing the risk of pregnancy.