I think you're right. I think she had no idea she was icing up.
I guess it's possible. Autopilot maintaining altitude so the AOA creeping up went un-noticed. Surprised she didn't get any accumulation on the windshield.
It'd be a hell of a wake-up call. Fat, dumb, and happy, cruising along until it all suddenly goes to crap. Lucky that enough ice got shed before she hit the ground. Glad it wasn't me.