This is the 5347th most frequent Spanish word.
llenas
"Full" (feminine plural).
In this sentence, "llenas" describes a state of being filled in relation to feminine plural noun "cajas."
Las cajas están llenas de libros.
The boxes are full of books.
Here, "llena" is used to indicate the speaker's emotional state and agrees in gender and number with the first-person singular subject "me."
Hoy me siento llena de gratitud.
Today I feel full of gratitude.
In this context, "llenas" describes the condition of the feminine plural noun "calles," indicating the crowded nature of the festivities.