If you are fascinated with Alzheimer's or are in love with Meryl Streep's phenomenal talents playing an Alzheimer's patient, see Iron Lady. If you have any interest in Margaret Thatcher as a person or leader of Great Britain, don't expect any of that in this movie. The non-Alzheimer's flashbacks probable amount to less than 20% of this disjointed movie, and are designed to conceal any utility of her policies or actions, such as when she is portrayed as viciously attacking the poor Argentinians despite the advice of her admirals.
In short, it is clear that Mrs. T and her politics were repugnant to the writers and producers, who are using Streep's fabulous talents in one of the more effective hatchet jobs (fortunately, the hatchet was so blunt the agenda is obvious to all).