Learn French: Sa fille est née en mars. - His daughter was born in March.

In French, possessive words like sa (his/her/its) agree with the noun that comes after them, not the person who owns it. Because fille is a feminine noun, we must use the feminine form sa. Sa fille can mean either "his daughter" or "her daughter" depending on the context!

Why does this sentence use est instead of a for the past tense?

The verb naître (to be born) describes a change of state. In the passé composé, special verbs of motion and changes of state use être (to be) as their helping verb instead of avoir (to have). Because of this rule, we say est née instead of a née.

Why does née have an extra "e" at the end?

Because this sentence uses être as the helping verb, the past participle (né) has to match the subject, just like an adjective does. Since sa fille is feminine and singular, we add an extra e to the end to make it née.

Is en always used for months like mars?

Yes! To say something happens "in" a specific month, you always use the word en. For example, en avril (in April) or en octobre (in October). Also, notice that month names are not capitalized in French!