"She likes water."
Translation:היא אוהבת מים.
No cuz that would be love water and you have to a person for example הוא אוהב מים or היא אוהבת מים
Both are for singular female, but different "person" mode.
She (3rd person) is היא. But את is "you" (2nd person), when you are talking to a single female. Use היא when you're talking about a single female.
There is no subject in your sentence. I guess maybe in an imperative sentence it might be ok.