Ok so a letter for an excuse not to come to school? I got you! This is if your parents are writing it but if your writing is just change it up a bit!
Dear mr/ms
I regret to inform you that my daughter is unable to attend school today as she is dealing with women problems. I would like to apologise if this causes any inconvenience for my daughter having to take time off school but her health and well being should always be put first. I trust that the school would agree that the well being of students are very important! Thank you for understanding!
Many thanks (name) mother