Well ...... like, I suspect, MOST of us contributing to this thread, I'm no authority on political matters.
So ... based on my [very] limited knowledge of the topic in hand, here are four notable achievements that spring to mind ...
... as a force for change, she:
(i) o Hauledout of the economic quagmire of the 1970s, by facing-down the NUM in prolonged, disruptive strike action which - while ostensibly about pay and conditions - had, in effect, been instigated to stir up mass discontent throughout the nation.
(ii) o Reformed the Trade Union Movements to allow the democratic methods of secret ballots, thereby lessening the possibility of coercion.
(iii) o Provided a role model for "championing" the efforts of individuals prepared to work hard to achieve success.
and
(iv) o Collaborated with the incumbent US President, Ronald Reagan and Pope John Paul II in contributing to the downfall of Communism.
was in late 1992 ... long after her resignation.