My sister had a similar situation at a retreat. The woman, who was a guest and not a member of the guild, talked incessantly about anything and everything and also had a nasally voice which made her prattling worse. My sister put on her headphones and turned the volume up so she would not have to listen. The woman was asked not to come to another retreat. I stopped going to a sewing program at the local sewing business. It was monthly and there was always a teacher/presenter who reviewed new patterns and books and actually made projects from them. Instead of losing my cool and telling them to "shut the hell up" I did not join again. We paid a yearly fee for this and so it was not worth it to have these rude women yacking through the entire presentation - rude to the audience and disrespectful to the presenter who put a lot of time into making the samples. I would be firm, but not nasty, and tell the person that everyone at the retreat paid for their spot and their time there was their own.