This is the 4126th most frequent Japanese word.
モニカ
"モニカ" (Monika) is a Japanese transliteration of the name "Monica."
Here, 'モニカ' is used as a proper noun, specifically a name for a person.
モニカは友達と公園に行きます。
Monica goes to the park with friends.
In this sentence, 'モニカ' functions possessively to indicate belonging of the smile to Monica.
モニカの笑顔はとても素敵です。
Monica's smile is very lovely.
The term 'モニカ' acts as the object of the preposition indicating the receiver of the action.