This is the 11835th most frequent Russian word.
замороженной
Frozen.
Here, 'замороженной' is used in the instrumental case as an adjective to describe the state of the fish when it was bought, explaining that it was frozen.
Я купил рыбу замороженной, чтобы сохранить её свежесть.
I bought the fish frozen to preserve its freshness.
In this sentence, 'замороженная' is an adjective in its nominative case, modifying 'пицца', indicating that the pizza being referred to is frozen.
В морозильнике лежит замороженная пицца.
There is a frozen pizza in the freezer.
'Замороженной' is used in the instrumental case to describe the associated 'улыбка' (smile), implying it is figuratively frozen or expressionless.