Being able to read is simply TOO fundamental a skill to be lacking.
And I'm saying that in a world where you can link contact lens cameras to computer powerful enough to run AI-level optical recognition software (which, per these pages, we know such an AI can be housed in a human-sized system) and radio the words back to an ear-piece communicator...lacking the ability to read can be worked around until Cass can be taught to read on her own.