Quick bit of help about refunding a lovely customer please

Hi everyone I hope someone can help me - I will be brief.

A customer has bought my items a few times over the last year - they’re a lovely customer who is homebound. Last week they bought again but ordered the wrong colour. They messages me today saying they’re sorry but can’t do a return / refund. So instead they made a new order today for the right colour.

I want to do more for this customer and refund the money for the previous incorrect colour order (and they can just keep the incorrect item it’s fine) and obviously I will ship out the correct order made today as normal.

What error code should I use to refund the previous order WITHOUT having the headache of either A) Opening a can of worms with forced returns and B) Causing her or me headaches with weird metrics and such

Any help greatly appreciated

Thanks

Sam