。
She baked three cakes.
Literal
She [topic-は] cake [object-を] three [counter-個] baked.
個 is the catch-all counter for small, roughly round or compact objects — fruit, eggs, dumplings, balls, or in this case cakes — when no more specific counter feels right. Notice the bare placement: 3個 sits between the object and the verb without any particle attached. This 'floating quantifier' position is typical of Japanese — quantity expressions can drift to a position adjacent to the verb without taking their own particle, in contrast to English where the number sticks tight to the noun.