Negative PT

My friend had a fling and she is now 1 week delayed. She tried taking a pregnancy test and turned out negative. Is it early to take the test? She also gave birth January this year, previously had PCOS but had regular periods after giving birth. Idk what to advise to her since I knew my pregnancy right away and I have regular periods way before I got pregnant and gave birth. Hope anyone can help. #pleasehelp #advicepls