Non-profit overpayment query

I have overpaid a person by cheque. This person donated a larger amount and told me to deduct what she owed from that.

The issue is how do I show it in the accounts? She paid the hire fee herself. But as it is a running expense I had to show it and then show she donated some money.

Now I realise that she owes the non profit an amount so how can I show it in the books? I have deducted the csh donation making her donation less and added the full rent as a CR. But the overpayment I do not know how to balance it in the books. Can anyone help pls?