The guy has two good options.
First and best, be magnanimous and not sweat the girl. Gives the best chance for people to appreciate his work in the way he intended it, yea the girl will be fucking with the bull but oh well. He comes off as gracious and open minded. He can see the privately but he doesn't come off as a dick and people can choose to enjoy his work for the reasons he made it or not.
Second is take his bull and go home. He no longer has to withstand the hideous indignity of his work being mocked by a girl or people interpreting his art in a way he didn't intend. He looks like a cranky old asshole but at the same time, the pain is over.
He's taking a third path. Threatening to sue, raging against a little girl and all that she stands for, enhancing the add campaign, making his bull look like an even greater aggressor than he did all ready, making capital look like a bully and he's going to lose this fight. The longer it goes on the worse he will look and the more sullied the image of the bull will become.
It's a fantastic bull statue, powerful and awesome. The girl statue is cleaver an charming. No matter what happens, the little girl is going to win the day. Tim for Di Modica to decide how he wants himself and his work to be remembered.