overpaid jsa due to late payment from wages

my client has an appeal ongoing, she worked part time and got paid several weeks after doing the work, she stopped and started work but went back too the same employer each time, the NHS,
DWP say she has to repay the JSA it is taken into account in the week it is paid not the week it was earned, the client seems to be arguing that in the weeks it was paid

the client is arguing that even though she was on jsa when she was paid her actual work was several weeks previous and she seems to be arguing that even though she went back to the same employer when shifts became available she in reality she stopped work each time shift work dried up and started employment again when new shifts were available
any ideas ?????