My cousin sent a message saying how to reply to menstruation on birthday.

You can reply to your cousin: "I wish you a happy birthday, good health and a happy mood." Please say hello to menstruation for me. I hope her life is getting better and better. " This kind of reply is polite and decent, expressing your blessing and concern for menstruation, and also expressing your greetings to your cousin's menstruation. If you are near menstruation, you can add some thoughtful words, such as "Happy Birthday to Menstruation! Eat, drink and be merry today ~ ". In any case, when replying to my cousin's message, we should pay attention to politeness and avoid using vulgar and inappropriate language.