I saw her in NIGHT MUSIC at the Kennedy Center Opera House, circa Spring of 1974 I believe (or 75?) She was most effective, in an understated way, and clearly having the time of her life. She was small of stature, but not frail, and I remember her singing the part successfully. The show was not terribly at home in the cavernous opera house -- the Eisenhower would've been better for the designs and performances. (I don't like it at City Opera either -- it's a very intimate show.) I think it was likely Hamilton's last big thing -- no?
The productions was sound, with George Lee Andrews, non-speaking Frid on b'way, playing Frederick, probably in his early to mid-30s. He was too young, and it made the Anne/Frederick dilemma a bit odd. Jean Simmons was fine, but I recall missing the comedic brio of Glynis, whom I'd seen the previous summer in NY. After Simmons played the role, Desiree fell into similar hands. I saw Virginia McKenna in London -- sophisticated but dull. I still think Glynis and Liz Taylor are the best casting, though Taylor couldn't exactly shine in the poor film.
Hamilton seemed to be having the time of her life.
"I'm a comedian, but in my spare time, things bother me." Garry Shandling