Reason For Blood Clumps During Periods?

well I have a friend name Rachel and she says every time her menstrual cycle begins and she has to use the bathroom to like urinate she has clumps of blood she wanted me to ask you why is this cause and how can she stop it and is they cure for this or is it normal I told her it may be a blood clot am I right or is it something else. Thanks you very much sincerely: Rebecca s best friend Jessica