There's a HUGE difference between big and loud. In terms of being loud...maybe she's not the greatest example...in terms of big, round, huge, open sounds she is phenominal. Her belt is so unique, rich, and gorgeous. Having seen her perform MANY times, in many different venues on wildly diverse material, I will just say that she definitly has a "big voice".
Not that I'm old enough to have seen it, but I was under the impression that production was done in the park. I wouldn't expect many people to deliver un-amplified vocals over an orchestra in that situation (and with all the emotional intention that she always has...her rendition of Pirate Jenny blows my mind).
"For me, THEATRE is an anticipation, an artistic rush, an emotional banquet, a jubilant appreciation, and an exit hopeful of clearer thought and better worlds."
~ an anonymous traveler with Robert Burns