my mini mare did not take till 5 yrs of age. mini's seem to need to mature more before they are ready and when she does deliver, keep an eye on her, smaller pelvics, mini mares need more help than full size horses. my mom had to help my mare deliver, even if its just to push a foot loose. (my mares baby's hoof was stuck, my mom just touched it enough to pop loose) phoenix was throwing herself to the ground trying to get the baby to move, a little helping hand was all she needed to deliver a healthy baby.
good luck with your girl.