Julia is the one who unintentionally and unknowingly gives Henry the chance, but he is the one who takes it, so it's his fault, even if Maria only blames Julia. It makes sense to me that she would blame Julia, both because of her specific context (her problem is liking Henry too much and Julia being her rival) and because I think people in general prefer to blame women more than men (and in this kinds of situations in general), but I don't think that means Henry isn't the bother. I think this particularly because barouche!Maria was happy to be reminded of her importance as a soon-to-be wife to Mr. Rushworth. It happening again wouldn't have made her unhappy if Henry had left her alone.