That's understandably annoying to colleagues, who are obviously losing patience. (The word "stifle" gave you away.)
Since the current strategy, avoidance, doesn't seem to be helping, you're going to have to confront her about this.
That doesn't mean merely hinting. Correcting this sort of person indirectly ("let's get back to what we were discussing") won't work. She's likely to experience such comments as interruptions of her monologue. Instead, someone—preferably her supervisor or a colleague who has enough of a relationship with her so that constructive observations aren't rejected out of hand—should talk to her privately.
Politely but firmly, tell her that her work is valued but that she may not realize how much she turns the subject to herself. Explain that "it derails conversations, and people have started avoiding you because they feel you don't listen." You'll need to keep your contempt in check. Otherwise, she may make that the subject of your talk, once again hijacking the discussion to meet her needs.I just left a job where my boss constantly put me on the spot, frequently demanding, for instance, that I settle disagreements between him and someone who was also my superior. What should I have done? — Anonymous, Los Angeles
You've already taken steps: You left. Others stuck in this dynamic might begin to address it by asking themselves if they are subtly offering themselves up as pawns—as a way of feeling at least a bit important. And a boss like this? Maybe he can't take responsibility for difficult or uncomfortable encounters. Maybe he takes sadistic pleasure in a making a subordinate squirm.
Whatever his problem, if you get into this situation again, try appealing to your superior's ego while enlisting his guilt: "I need your guidance. I'm in an awkward situation here, trying to mediate between the two of you. How would you advise me to handle it?" It's a long shot, but if your supervisor has enough empathy to see the problem he's created, it can make a difference. If not—well, sometimes we have to accept the unlikelihood of change in someone on whom we're dependent. And separate from them. Kerry J. Sulkowicz, M.D., a psychoanalyst and founder of the Boswell Group, advises executives on psychological aspects of business. Send him questions at email@example.com