Responsa על בבא בתרא 261:2

Q. Before marrying his second wife, A stipulated, in the presence of witnesses, the following condition in his agreement with the sons of his first wife: The sons that will be born from the contemplated marriage shall share equally with the sons of his first marriage in the inheritance of his estate. Subsequently A married and his second wife bore him a daughter. Before his death A sought witnesses to attest to his will that his daughter should inherit part of his estate, but he was overtaken by sudden death. Are we to assume that in the agreement referred to above A intended to give to a daughter the status of a son?
A. The term "sons" when used in vows does not include daughters. Moreover, a person who has sons has no right to give his daughter the status of an heir. Therefore, A's daughter is not entitled to the share of an heir in A's estate.
SOURCES: L. 236; Mord. B. B. 603; Agudah B. B. 190; cf. Sinai IV (1941) 10, no. 88.