Well, I didn’t mean it disparagingly, as I’m a fan of hers, but the fact is that early in her career she worked with a famous speech coach because some considered her speech not refined enough.
No, but public speeches are also rehearsed. In the early days of audio recording, public figures made a point of altering their natural speech when they thought they had to make a “good impression.” I think she did always have a basic, natural upper-class Connecticut accent, but as someone with extensive stage training she was hyper-aware of how she she spoke in front of a microphone, and enhanced it. All I really meant to say is that how she spoke in movies should be taken only with a grain of salt as representative of any American accent.