http://revach.net/article.php?id=1867

Section: Halacha   Category: Tshuvos
Rav Moshe Shternbuch: Your Daughter Became Bas Mitzva, Boruch ShePatrani!
When a boy becomes Bar Mitzva the father says the Bracha of "Boruch ShePatrani MeiOnsho Shel Zeh" thanking Hashem for relieving him of his son's aveiros and thankful that his son is now an independent adult (at least halachicly).  What about when a girl is Bas Mitzva, shouldn't the bracha be recited for the same reason?

Rav Moshe Shternbuch says (1:156) that among other reasons mentioned by the Poskim for not saying the bracha on a girl is the fact that this bracha is customarily made in Shul by Krias HaTorah in front of many people.  The wording of the bracha is "Shel Zeh", which specifically refers to the child who therefore must be present at the time of the bracha.  Since it is not proper to bring your daughter into shul the Chachomim were not Misaken to make this bracha on a girl.

Important Note: We try to convey the Tshuva to the best of our ability. We admit that our understanding may not be accurate. Please also understand that this Tshuva may not be the final word on this topic. One should consult a Rav before drawing any conclusions.