Are there any particular times at which your friend wants to travel, and does your friend have any railcards?
Without a railcard, the not via London Off peak period return is £93.60.
But there are some through "Advance" (i.e. booked train only) tickets.
Outward via Norwich, Nottingham and Derby there are through Advance tickets at £44.50 on the 0950, 1350 and 1550. Journey time is about 5 hrs 45 mins. Or a £43 advance via Ely & London on the 0950 with a similar journey time.
Returning, there's a through Advance ticket at £28.40 on the 0724 via Derby, Nottingham and Norwich.
It may well be possible to reduce the cost further by buying different advance tickets for different parts of the journey, but I don't have time right now to work out what might be possible.
Trainscanbecheaper suggests the following flexible tickets:
Lowestoft-Peterborough £24.80 offpeak period return
Peterborough-Blythe Bridge (which is between Derby and Stoke) £29.20 offpeak period return
Blythe Bridge-Stoke-on-Trent 2 x £2.90 singles
Total £59.80 but only valid for travelling via Peterborough and Derby and only valid on trains that call at Blythe Bridge and not valid on some morning trains (i.e. not before 9am) on the journey back.