This is the 798th most frequent Czech word.
zůstala
"Zůstala" means "she stayed" or "she remained" in English.
Here, "zůstala" indicates a state of remaining or staying after something else occurred.
Po odchodu všech hostů zůstala sama doma.
After all the guests left, she remained alone at home.
Here, "zůstala" refers to the state of remaining in a specific condition, in this case, the gate staying locked.
Ujistili jsme se, že zůstala zamknutá brána.
We made sure that the gate remained locked.
In this sentence, "zůstala" describes the condition of something that did not change, specifically staying dry.