Yes, she can refuse to be the executor. If your grandfather did not select an alternate in the event his wife refused to be the executor, then the court can appoint someone in her place. You will need to check with an attorney in your area to see what the law requires.
Lucreita D. Becude is correct, but I am wondering whether you are asking whether your wife can ignore the terms of the will. The answer is that the terms of the will must be followed.
Hope this helps.
Mr. Fromm is licensed to practice law in PA. The response herein is not legal advice and does not create an attorney/ client relationship. The response is in the form of legal education and is intended to provide general information about the matter within the question. Oftentimes the question does not include significant and important facts and timelines that if known could significantly change the reply unsuitable. Mr. Fromm strongly advises the questioner to confer with an attorney in their state in order to ensure proper advice is received.