Both ein and eine are the indefinite article forms (a/an). But ein has to be used before a masculine or neutral singular noun while eine has to be used before feminine singular noun. Examples: ein Pass(a passport - Pass is masculine), ein Auto(a car - Auto is neutral), eine Wagen(a vehicle - Wagen is feminine). These apply only while dealing with nominativ nouns(subjects). If you want to apply the indefinite article forms to objects in your sentence you have to change the masculine a/an to einen instead of ein and the rest are all same.

Eine is female.