Is it permissible to offer a female animal as an udhiyah?

With regard to the udhiyah, it is stipulated that it should be an an‘aam animal (i.e., a camel, cow, sheep or goat), free of defects, and of the appropriate age as ordained by Islamic teaching. There is no difference in that regard between male and female, so it is permissible to offer either as an udhiyah. 

An-Nawawi (may Allah have mercy on him) said in al-Majmoo‘ (8/364): 

The condition of the udhiyah being valid is that it should be one of the an‘aam animals, which are camels, cattle and sheep (and goats). All types of camels, all types of cattle and all type of sheep and goats are acceptable. It is not acceptable to offer anything other than an‘aam (livestock) animals, such as wild cows, wild donkeys, and so on, and there is no difference of scholarly opinion concerning this point. It makes no difference whether the animal is male or female, of any of these types. There is no difference of opinion among us concerning any of these matters. End quote. 

The scholars of the Standing Committee for Issuing Fatwas were asked:

Tell us about the udhiyah: is it acceptable to offer a six-month old sheep, as they say that it is not acceptable to offer a sheep or a lamb unless it is one year old. 

They replied:

With regard to the udhiyah, it is not acceptable to offer a lamb unless it is over six months old, regardless of whether it is male or female. It is called jadh‘an because of the report narrated by Abu Dawood and an-Nasaa’i from the hadith of Mujaashi‘ who said: I heard the Messenger of Allah (blessings and peace of Allah be upon him) say: “A jadha‘ (six-month-old sheep) is acceptable (as a sacrifice) for what a two-year-old goat is acceptable for.” A goat, cow or camel is not acceptable unless it is of the appropriate age, regardless of whether it is male or female. In the case of goats, it is that which has passed the age of one year. In the case of cattle, it is that which has passed the age of two years. In the case of camels, it is that which has passed the age of five years, because the Prophet (blessings and peace of Allah be upon him) said: “Do not slaughter anything but a two-year-old animal, unless it is too difficult for you, in which case slaughter a jadh’ah sheep.” Narrated by Muslim.

End quote. 

Fataawa al-Lajnah ad-Daa’imah (11/414)

For more information on the conditions of the udhiyah, please see the answer to question no. 36755 

And Allah knows best.