Ah … just to jump in with MHO …
First off, at least to me, and I assume the OP, “little girl” voice is Not the same thing as “high pitched.” High pitched voices are another matter, all together, when I think of “little girl” voice, on an adult, I’m thinking of voicing and inflection and pitch placement that actually sounds like a very young child, even if the diction if perfect.
It has certainly seemed to me that when the speech development got arrested at a very early age, given the chance to explore, you’d find there was some form of trauma at that point in their development.
This is not different from any other part of the personality becoming arrested at a young age, like the classic adult “boss” who throws 5-year-old temper tantrums when things don’t go his way, just that part of their emotional development got “arrested” or stuck, and it fell behind the rest of their growth. (Or I guess an equal example could be my own 13-year-old humor … dunno the trauma, but I’m find the “body parts and farts” part of my humor is still Very Much alive and well…)
It’s been my hunch that early sexualization would be the most likely event to make speech development ‘freeze’ in baby or very-young girl, but I’m sure that even a shocking loss could do the same thing. So, I wouldn’t assume molestation, when I heard a baby voice in an adult woman. I have, however, heard significant, and relatively sudden, changes in speech patterns when women have managed to “bring up to current time” some part of “their inner child” that got stuck, reviewing and trying to “make sense” of some childhood event that was a ‘senseless’ trauma.
And all seriousness aside, this picture REALLY cracked me up!
I have a friend who ‘normally’ has a solid alto speaking voice, but sounds just like a smurf when ever she reads anything out loud! I’ve mentioned it to her, and she can’t hear it at all! Cracks me up. (though I quit saying anything to her, it just frustrated her … but it is funny to hear a news story read over the phone by one of the smurfs!)