Thank you for your replies. I was a bit concerned that she would end up with half an hour of extra time at the end, with nothing to fill it.
She will make the icing at home and bring it in three containers.
After the introductory talk, she wants to divide the brownies into tables, with a table for each six. They would then start the friendship bracelets. While they are making these, she will prepare a paper plate for each table with three colours of icing in cupcake cases, using the kitchen (there's a large hatch facing the brownies, so she'll still be able to see them).
Once nearly all the brownies have finished the bracelets, she will hand out the quizzes, one for each table and pencils. While they're doing the quiz, she will finish getting the icing ready. Once everyone has finished the quiz, she will get them to swap their answers with another team, read out the answers, find out which six won and congratulate them (do you think she should provide small prizes for the winning six or is this not necessary?)
She will then ask each sixer to collect the biscuits and icing materials for their table from the hatch. While they are icing the biscuits, she will get out an extra table for them to leave the iced biscuits on (on paper napkins). At the end of this activity she will ask each six to return their unused icing to the kitchen and wipe their table. She is hoping that the brownies will be able to fold away their own tables, but all the usual leaders (plus her Guide leader) will be there to help.
If there is time left, she is then going to show them a game which they will all play together.
At the end of the meeting, she will hand out copies of a traditional blessing, which they will all read out together.