The director fired the worker. She was known to be aggressive.
please tell me the right answer
It is impossible to tell who "she" refers to.
"She" ought strictly to refer back to the most recent of the possible referrents, i.e. "the worker". However, in practice, the sentence is ambiguous and ought to be rephrased. Of course, if we knew that only one of the two people involved was female, that would remove the ambiguity.
I agree with Robert Jones. Besides the first sentence itself is telling us the worker could be aggressive. Why may the director be aggressive?. To fire someone doesn't tell you are aggressive (maybe just a bad person XD).