It sounds to me as if she's trying to suss out what appropriate boundaries are--and not only what she feels comfortable with, but what DD123 is comfortable with. I suspect she's trying to figure out if doing that sort of thing is going to work well within the relationship she has with DD123.
When speaking of various forms of non-monogamy...it ain't poly if you're just fucking around.
While polyamory, open relationships, and swinging are all distinctly different approaches to non-monogamy, they are not mutually exlusive. Folks can, and some do, engage in more than one of them at a time--and it's all good.