Is it necessary to offer two sheep as 'aqeeqah for a girl after a prior intention to do so, or one sheep as stated in the Sunnah?

The basic principle is that one sheep is sacrificed for a girl and two for a boy, however, it is authentically reported that the Prophet, peace and blessings be upon him, sacrificed one ram for Hasan (definition) and one ram for Husain. There is no objection to sacrificing two sheep for a girl, as there is flexibility in this matter. Imam Al-Shafi'i considers the number to be a Sunnah (definition), while the Malikis do not consider the number in the Aqiqah (definition).