Really what she is describing is the development of her self-consciousness, self-image, self-awareness, and awareness of the process of thinking within that, that comes from being introduced to language.
On the wikipedia page for her there is a quote:
I stood still, my whole attention fixed upon the motions of her fingers. Suddenly I felt a misty consciousness as of something forgotten — a thrill of returning thought; and somehow the mystery of language was revealed to me. I knew then that w-a-t-e-r meant the wonderful cool something that was flowing over my hand. The living word awakened my soul, gave it light, hope, set it free!
It is as if what she's saying is that the loss of her sight and hearing locked her away from a dim sense of who she was before.
Most of us can't remember things from 19 months old as adults and likely wouldn't have been able to remember them at the age of seven. But she was locked away with sense memories of her 19-month-old experience of the world for all that time.
Her writing really is fascinating and eloquent. It brings to mind Harold Bloom's theory that Shakespeare essentially invented a terminology and model for describing our inner monologues.
It depresses me that there will now be a phalanx of motivated reasoners trying to shoehorn her story somewhere into their projections onto the current technological obsession.