I don't have the link handy but it's entitled: "Helen Keller Speaks."
If you look at the video it seems she even appeared to pick up the accent of her teacher.
Tongue movements would have been harder to learn which explains why her vocalizations are hard to understand.
Yes, some people go through "speech therapy" and train to emit the right sounds while not hearing the output (but I think they rely on the inner vibrations ?).
Understandably that requires a ton of training on top of existing skills and not everyone ends up with something workable.
Part of the existing skills is the the ability to vocalize the sounds in the first place, and if a kid never intentionally vocalized for 11 years, I wonder if their vocal cords could ever develop to a point they can make the range of sounds needed.
I had wondered about this for awhile, how when you see adults have their cochlear implants turned on for the first time, sometimes they respond as though they do understand what people are saying to them. I had wondered how they could possibly know how to interpret the sounds as specific words, even if they knew the words, but this makes it seem like that's not what's happening. They're probably still reading lips to understand the words themselves.
I ask because I'm interested to know which parts of brain research might eventually try to prop that door open. Granted, most people born with this genetic condition would probably just be treated shortly after birth and learn spoken language during the normal time frame, not go through some special other treatment just to prop that mental door open, but I'd still be interested to understand what's actually going on in the brain better.