I think Theresa McCarthy is too young for Margaret, but that could be because I have an image of her as Kate Murphy (a.k.a. Kate 3) in Titanic burned to the back of my eyelids! But she has an amazing voice and I'll bet she could play all the female roles in Piazza; she's worked closely with Adam for a while and was a lead in both Myths and Hymns and Floyd Collins, so I'm sure she was involved in some small way with Piazza, though I don't think she was mentioned in the thank you's.
"Peace! The charm's wound up."
--Macbeth