A friend of mine would do very noticeable vocal fry at the ends of some sentences, when laughingly speaking light-heartedly and enthusiastically about something

A friend of mine would do very noticeable vocal fry at the ends of some sentences, when laughingly speaking light-heartedly and enthusiastically about something. She's also an MIT PhD, and I don't recall any vocal fry when speaking seriously about science or some other topic. Before I learned that vocal fry was a thing, I thought she might be code-switching to a regional or socioeconomic group accent from where she grew up in the US, or a mannerism that a particular friend group evolved in a more carefree time. Her voice sounded nice, and a little unique. And you don't want to ask, and risk making someone self-conscious about how they sound or look when they're happy or laughing. Whatever is natural is best.