Wait, still can't say anything but "gah", yet can describe a scene to that degree of clarity? Feels like R2D2 from Darths and Droids, where he took a flaw that he had no intention of role-playing.

We aren't getting the satisfaction of hearing her speak clearly, but a picture speaks a thousand words... so, somehow, she's doing it. We know that she was BEGINNING to be able to say words when we last saw her, so it's likely she refined that speech. Her "gah" is probably just a habitual verbal tic and go-to affirmation at this point, I'm willing to bet.