Tafsiran Kejadian 30:21: Rashi, Rashbam, Radak & Rabbeinu Bahya

דינה DINAH (Judgment) — Our Rabbis explained, that Leah set herself up as judge (דנה) against herself saying: “If this be a son, my sister Rachel cannot be even the equal of any of the handmaids”. She, therefore, offered prayer regarding it, and its sex was changed (Berakhot 60a).

ותקרא את שמה דינה. No mention is made of Leah giving thanks to the Lord for giving birth to a daughter, seeing that one does not express gratitude for bearing a daughter in the same degree as one does for bearing a son. The reason that the birth of this daughter is mentioned is to inform us that with the exception of this one girl Yaakov’s children were all males. The same thing is true of the daughter of Asher, Serach being mentioned; (46,17) among all the 70 Israelites descending to Egypt only two were females.

ואחר ילדה בת, it would appear that originally Dinah was meant to become Zevulun’s twin (brother). This is why the Torah wrote ואחר ילדה בת, without making any mention of Leah again becoming pregnant. The Torah did not even write ותלד עוד. No mention is made of why she named the girl Dinah. There is a well known aggadic explanation that Leah did not want her sister to be shamed in having fewer sons than even the handmaids; her prayer to that effect was answered by this fetus becoming a girl.