So I had lunch with this friend today and tried to tactfully express my concerns.
Long conversation short, she pretty much said she's a bit unsure about it, but that she loves her fiancé so she wants try. Apparently, when he brought it up, she told him she was a little unsure/uneasy about it, but that he pretty much told her that's the type of relationship he sees himself having with his future wife, period. She beat around the bush and said it more nicely, but that's the gist.
Now I'm more concerned because she doesn't even seem to want this. It seems like she's just doing it bc she's afraid to be without him, and since he probably knows that now that she agreed to do this, I can only imagine this decision is a slippery slope to a life of being taken advantage of and probably inappropriate punishments.