Protoevangelium (Genesis 3:15) translational differences

When reading on Biblical Prophecies, a big one is Genesis 3:15. The Douay-Rheims translation says > "I will put enmities between thee and the woman, and thy seed and her seed: she shall crush thy head, and thou shalt lie in wait for her heel." When it says "She shall crush thy head..." is it refering to Mary, Jesus, or the both of them doing so? Growing up as a Methodist, the Bible has always said "He shall..." and not "She shall..". Why is it translated the way it is?