Claudio publicly humiliated his fiancee Hero (who is Beatrice's cousin) by walking out of their wedding while publicly accusing her of sleeping around.
Well, they are both in the same play, Much Ado About Nothing. Benedick and Claudio are both soldiers in the same company; Hero and Beatrice are cousins. The men and women have the same type of...
Beatrice was upset about the way Claudio acted during the wedding when he accused Hero for being with another man. He hurt Hero and to that Beatrice felt that Claudio needed to be killed.