No way!
(In the term of surprise, not answering in the negative!)
I just did this yesterday in the "Prime Minister Hugh Gaitskell" thread. I think that if she was to emerge as Labour leader you would need to butterfly away Harold Wilson's Premiership and have a more moderate Conservative Party in terms of social values.
Under the Social Revolution of the 1960's, a strong Castle leadership bid could most definitely work. How she would fair as PM is a matter of some debate, but more than worthy of some thought. She was, after all, a very experienced and talented politician.