Going back on the discussion a bit, Diana did have her hair slightly longer for a spell - about the time of Harry's birth, you can see it in the newborn and christening pics.
If I remember rightly, it was roundly panned (press, commentators etc) and quickly lopped back shorter again. Probably lasted three months 🤔 - and wasn't even that long, but hinted at maybe where she was planning to go with it.
(Teenage me thought she was sooooo glam in the christening pic 😂)