I've only had the chance to see her live a few times, but my god, she is one of the most detail-specific actors I've ever seen in a musical. She's a work of art.
Her DOLLY was so far outside anything I'd seen her do before (ie., Fosca), and I went, in part, just to see if she could really do that kind of broad comedy. I was shocked at how well she handled it all. It seemed effortless for her, and she knew how to absolutely HAM IT UP when the role required it. I'm so sad I missed her WONDERFUL TOWN.
And I agree about that "Could I Leave You" performance. It's thrilling.