As Paul has said, £1.60 each way is correct for Zone 1, whatever the
time of day. Is it possible that she is changing from NR to LU outside
of Zone 1 (e.g. at Stratford instead of Liverpool Street), without
realising that this is costing more?
--
Paul Terry

Thanks again for the info. I'm afraid I can't provide any evidence, only
that her balance seemed to be less than expected the next time we used the
Oystercard.
At least this issue is being addressed in the latest leaflets.

John