Peggy is a feminist icon by accident, because she scales the career ladder flawlessly while just happening to be a woman. When she gives up her baby at the start of Season 2 to pursue her career, she makes a choice unconsciously facing many modern women (who, thankfully, mostly avoid the pregnancy altogether thanks to modern medicine) but also a choice to prioritise work over every other obligation that faces many people, male and female alike. She displays assurance, perseverance, determination and steely resolve. She is innovative, quick and clever, asking all the right questions and learning from all the mistakes she makes.
And all this is made more noteworthy because she's a woman.
Peggy is a feminist icon, there's no doubting it. But (as Lucy Mangan points out in her excellent Stylist piece) she does this in a time before feminism even existed. Peggy saw what she wanted and went for it, through hard work and determination. The fact that she becomes a (albeit fictional) trailblazer as a result of her possessing ovaries is of tantamount importance. But Peggy's story is inspirational to everyone - young and old, male and female. The story of a determined and committed young person learning, making mistakes and learning some more, seizing opportunities, and never being content with anything less than what she wants.