What is Margaret Thatcher best known for?

Margaret Thatcher, often referred to as the "Iron Lady," is a monumental figure in British political history, primarily remembered for breaking a significant barrier. While the other options touch on important aspects of women's rights and contributions, they don't align with Thatcher's specific achievements. The fight for women's suffrage occurred much earlier, with figures like Millicent Fawcett and the Pankhursts leading the charge in the late 19th and early 20th centuries. Similarly, modern nursing's foundation is attributed to Florence Nightingale in the mid-1800s. Thatcher's claim to fame rests on her premiership. She served as Prime Minister from 1979 to 1990, making her the longest-serving British Prime Minister of the 20th century. More importantly for this question, she was the first, and so far only, woman to hold that office. This achievement alone makes her a pivotal figure, regardless of one's political views on her policies.