From the Internets:
a) In R. Yosef’s article/teshuva on this subject published in Shonoh
Beshonoh (tashmag, a Heichal Shelomoh pub) he cites a string of fellow
bas mitzvoh posikim approvers, including the Ben Eash Chai (Re’ay 17),
R. Mosfia (above), Yascil Avdi (Orach Chayim, 28), and the Siriday Aish
(siman 93), and Nitivei Am (siman 225).
b) He cites R. Moshe Feinstein’s negative opinion to specifically
disagree with it. In particular, he cannot understand why R. Moshe would
distinguish between the celebratory requirements of the boy and girl
based on the different levels of “hecair” or public recognition that is
associated with the entering into obligation (e.g. the boy’s public
participation in minyan, etc.) He asks how could R. Moshe make such a
differentiation without any established basis, when the clear
celebratory requirement is chal with the entering into the obligation,
equal for boy and girl, and not dependent on later form of
performance. He also cites the harmful effects of appearing to
“discriminate” and the Siriday Aish’s similar perspective.