Yes! For some women, periods are extremely painful and can even lead to fainting. Also I really don't understand how blood leaking out of your vagina for 4-7 days has anything to do with feminism. Females have to deal with periods because its a biological process, not because of "feminism". Sometimes periods are really messy and can cause painful cramps. It is not fun to be on your period. Depending on the woman, it can be the one of the worst pain ever.
As long as the woman has a doctor's note, it should be valid reason.