This is the 106th most frequent Polish word.
ją
"Her" (accusative form of "she").
In this sentence, 'ją' acts as the direct object. It is the accusative form of 'ona' referring to 'her'.
Zobaczyłem ją w parku.
I saw her in the park.
Here, 'ją' is used as a direct object in the sentence, again the accusative case of 'ona' to signify 'her' being seen.
Widzę ją codziennie rano.
I see her every morning.
In this example, the word 'ją' serves as a direct object in a part of the sentence to mean 'her,' specifically the one whom I like.