The meeting I go to has a similar situation. One member arrives late, monopolizes the meeting with her successes/opinions/needs/unrelated-to-weight-loss stories, then, when the meeting (which is running late at this point) gets back to topic or other people finally get to share, she gets up and leaves!
However, she doesn't bother me as much as the two people who have had private conversations during the last two meetings. It's a small room so even murmuring is distracting. Our leader gives it her best shot to rein them in, but she hasn't been too successful.
I admit I'm tempted to sit next to them so I can intervene myself, but I'll probably continue to keep as far from them as possible!