All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
Menstruation is one of the signs of maturity as we have mentioned in our Fataawa 83431 and 87018.
As long as your daughter has reached the age of puberty she has to fast and you should force her to fast if she does not want to fast during the month of Ramadan.
Saying that it is hard for her or that she cannot concentrate on studies is not an Islamicly valid reason not to observe fasting as we mentioned in our Fatwa 89317.
Allaah Knows best.