Well, she IS almost 100, so while HYDRA could have instigated her mental breakdown, if they were patient all they really had to do was just wait for nature to take its course. Poor Peggy.

In any case, I basically agree with recessional's take on Pierce, that he's extremely hard to recognize for what he really is because he's actually sincere, and on top of that, sincere in ways that probably would've appealed to Peggy quite a lot. To her he would have seemed like a bright young kid out to make the world better, and I can definitely see her offering him a helping hand as a mentor once she met him, which is both fascinating and horrible to think about.