LOL, you guys are taking this way too seriously.
It's obvious that Agent 13 is Sharon Carter and VanCamp is playing her. Now maybe they change her relation to Peggy, but something tells me there will still be a familial relation. I don't really see a resemblance between the two actresses, but why does that even matter?
Peggy is like 90 now and probably looks nothing how she did in her 20's