CE Level 2: 1st Declension

puella, girl (feminine)
case singular plural
nom. puell-a puell-ae
acc. puell-am puell-as
gen. puell-ae puell-arum
dat. puell-ae puell-is
abl. puell-a puell-is

All CE Level 2 1st declension nouns are feminine unless they refer to male people.

There is wide scope for confusion with the –ae ending. Use the rest of the sentence to iron out ambiguity.