I think there's almost 20 minutes unaccounted for in the timeline.
At 3.23pm she is leaving the cathedral grounds and at 3.49pm (26 minutes later) she is near the Playhouse on St George's Street. This is only a 7 or 8 minute walk at an average pace, and using any of the three most logical routes between points, according to Google maps, leaving about 18 or 19 minutes spare.
Norwich Cathedral to The Playhouse Bar
timeline in article -
Mrs Lord walked out of her workplace at Jarrolds department store over an hour before her shift was due to end and hurried through the streets of Norwich on December 8.
www.dailymail.co.uk
I wonder if she stopped and looked at the river before crossing it.