I listened to the audiobook it was free on BBC Sounds at the time. It was read by Anne Dowd (Aunt Lydia) who was fantastic. I really enjoyed it, not as hard hitting but complements the series well.
Yes, I recall that A. Lydia is one of the Narrators and Nicole and Agnes (Hannah) are the others. I believe they are all instrumental in bring down the Gilead regime some 15 years after present-day events.