People have a First Amendment right to own and display offensive posters.
It is a crime to steal someone else's property.
Your parentage or her life experiences do not confer on you or on her the authority to infringe on anyone else's constitutional rights or to steal anyone else's property.
Political correctness has it’s victim group pecking order. Jewish Americans are not at the top anymore. In the past, the media would go on a witch hunt rip over these posters and the old lady would not have had to do anything.
But I agree that nobody should take it upon themselves to cleanse the public square of political speech and advertising they do not like. When she sees a poster she doesn’t like, she knows not to vote for the idiot who put it up. She is free to put up posters in opposition to political speech she dislikes.
They should have posed him as Stalin or a jihadist on the poster.
On their own property.