Is it permissible for a mother and her unmarried, financially capable daughter to share the cost of the Udhiyah (sacrificial animal)?

It is not permissible to share the cost of a single sheep for an Udhiyah (sacrifice). However, for a camel or a cow, up to seven people may share in it. It is sufficient for a person to sacrifice one sheep on behalf of himself and his household, regardless of their number.