This is the 1643rd most frequent Spanish word.
llena
"Llena" means "full" in English.
The word 'llena' is used as an adjective to describe the state of the bottle being full.
La botella está llena de agua.
The bottle is full of water.
Here, 'llena' (masculine form is 'lleno') indicates that the day at the park abounds with fun, metaphorically filled.
Cada día en el parque está lleno de diversión.
Each day at the park is filled with fun.
In this sentence, 'llena' functions as a verb in third-person singular, meaning 'she fills'.