What provision, if any, did she make for her pet in her will? If she had no will, her property passed to her heirs at law. As an exhusband, you aren't an heir. If she left an administrator of her estate or an administrator, contact that person and ask about the pet.
I am not intending this to be legal advice, because I don't know the particulars of your situation. Call me if you would like to discuss this or other isues.