No, but "pants" and "knickers" are both British English for what we call "panties" or "underpants."

I agree re: pants, pajamas, and pajama bottoms. Also, if she were wearing shorter pajama pants, you could say "pajama shorts" or, sometimes, "boxers." "Boxers" usually refers to men's underpants, but there are certain kinds of women's pajamas that are styled similarly and have the same name.