Sharon stood there for just a brief second before she decided this had been a terrible idea and decided that she was the least person qualified, and definitely the last person that ought to be explaining what was going on here. Not for any reason other than what sort of things weren't even accurate across timelines? Did this Peggy even have any siblings? She could barely even imagine how strange this must be, and was she really signing up to continuously bring the weird/bad news to the people she cared about? Nope. Nope. Definitely not.
So she was about to just say she thought she was someone else, apologize and let her be on her way. But she was obviously new here. "My name is Sharon Carter. I'm Peggy Carter's niece, it's 2015, and I'm sorry for accosting you on in the park I'm just," pause, "Really happy to see you and I really love your shoes," she said smiling a bite wider. with a bit of a shrug. What the hell else was there left to say?