I appreciate your honesty and I think my mom would, too. She respects you a lot so I think she would be very understanding if you address this concern directly with her. If you prefer to call her, her phone number is [...]. (She's out of town until Wed. though.)
That said, if you think that it might be more of a benefit to the group to ensure that no one person in general would "dominate" a discussion, maybe--and I don't know if it's worth proposing to [friend's name] because she is the book club coordinator?--at the top of the next meeting we could take a few minutes to decide as a group on a few rules that might help everyone be more at ease.
Just my thoughts.
UPDATE (9:27 p.m.): I've been avoiding my e-mail since I sent it, but about an hour after I replied, Leona sent the response below. . . my comments in bold.
Ok. Let's try your idea [I assume she means my brilliant "save it for group" idea]. I don't know her well enough to say anything [uh, TO HER FACE, anyway!] and would not want to hurt her feelings ["at least not directly which was why I was trying to foist it off on her daughter"].
Let's see how it goes. It should be fun [on what planet is creating rules to prevent people talking too much FUN!?]. Thx [she doesn't mean that, either].
She was probably shooting daggers with her eyes at the screen while she was typing that.
Well, then, I am just going to let this marinate among her and whoever constitutes the "we" of her previous ignorant e-mail, and see what happens at the next meeting. (I've got you all on the hook for that, now, don't I?) It's not until the end of AUGUST. And you may recall that my mom (she of the five plus sentences) is hosting.
Oh, can they really keep it contained for that long?
Stay tuned, kiddies.