I have been thinking of all you kind folks ever since I posted with worries about my infant son some months ago on the development board. I occasionally check in to see how everyone here is doing. (Congratulations, Jimjams!) I recently came across the story of a boy from India, now in the United States, who sounds very similar to the girl you're describing here. I wanted to share it with this board in case it is helpful for anyone here.
The boy's name is Tito, he's 15, and he has very severe autism, but can communicate by typing and even by handwriting. This kid is brilliant, though one would never know it if it weren't for his writing...he says has an intact mind inside of a "disobediant body" and is able to describe in beautiful detail what it is like to be him. Like Lucy, it is mostly sensory issues which make him seem so unreachable. His mother through years of effort taught him to point to a letter board, to type, and eventually even to write with a pencil. (She had to do the pencil because folks doubted that Tito was really communicating via any of the other methods she had tought him.)
He has had a lot of media coverage lately so you not only read his story, but also see him on video. Here is an episode of Closer to Truth and an episode of 60 Minutes . And this is some of Tito's writing . (The writing requires Adobe Acrobat Reader).
His mum is going to be developing training materials on her methods. Unfortunately, it sounds like it's going to be very commercialized, but it does seem to be for real. Here is a video of a 5 or 6 year old learning to communicate. I was amazed when I watched it.
The folks in the US who brought him over from India are a married couple who are autism advocates and parents of an 11-year old son with autism. In a pretty short time of training with Tito's mom and her "Rapid Prompting Method" he was able to communicate with them for the first time...and it turned out he had been listening and understanding them all along...just couldn't bring his body to respond. I guess the methodology has a tiny bit in common with ABA, but it's more based on continually prompting the child to stay focussed on the task at hand, even through stims and disturbing sensory input and other distractions.
Anyway, hope this is helpful in some way for someone. I know there's a lot of snake oil out there, but this one seemed worth posting.