Welcome to the site.
Thalassemia major prognosis is excellent with the current medical advancement. It is possible to get married and get pregnant with thal major. Infact, lot of our thal major members are married with children and living healthy lives. Do not worry, keep chelating your girl and make sure she gets her transfusions regularly. Good Luck.
The requirement of blood will increase when she would hit puberty, however, the amount of extra blood varies in different people, I don't thnk it would increase tremendously though. The blood loss from the period is not a bad thing in Thal major, as it is also a source of iron excretion as well.
Bone marrow, a possible cure for thal major is a serious decision that has to be considered by parents only. We have some members whose children are cured, however, there are some complications that may arise as a result of Bone Marrow.
Please keep posting and ask more questions, specially all your concerns.
Feel safe here.