The thing I find most troubling is the lack of trust she shows B. If that can't be worked out, then there's really not much hope for that relationship and her issues will emotionally drain B and anybody else who is close to either of them. Not only will that toxic element rot out their relationship, it can affect the relationships of everybody close to them in any fashion.
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.