filia

Filia, filiae is feminine, first declension, and regular except in one place that matters. The dative and ablative plural is filiabus rather than filiis, kept separate so that a will leaving something "filiis et filiabus" cannot be read as leaving it to the sons twice. Dea and deabus do the same job for the same reason, and so do liberta and nata.

Roman daughters took the family name in feminine form and no personal name at all, so every daughter of a Claudius was Claudia; two of them were distinguished as Maior and Minor, three by number. English filial and affiliate come from the masculine, and the Romance forms, French fille, Spanish hija, Italian figlia, all descend from filia directly.