There are three families \( F_1, F_2, F_3 \). \( F_1 \) has 2 boys and 1 girl; \( F_2 \) has 1 boy and 2 girls; \( F_3 \) has 1 boy and 1 girl. A family is randomly chosen and a child is chosen from that family randomly. If it is known that the child is a girl, the probability that she is from \( F_3 \) is