I think by saying only "true ladies" do something, you're denigrating the women who don't do those things. We're all ladies, even if we don't wear pantyhose. I don't wear it, regardless of the weather. I hate it. I don't really think there's one good answer to the question. Some women live in warm climates where pantyhose isn't necessary. Others live in very cold climates where it is. It's personal preference really, not a hard and fast rule. You're no less of a lady for not wearing it than you are for wearing it.
BTW, those aren't sandals she's wearing. Those are strappy heels. Sandals are flat shoes you usually wear in casual situations, like to the beach or on the boardwalk.