I get paid child support (when he feels like it) and I was made redundant in Nov (a few years ago).
The only reason I paid no tax on my redundancy payment is that I came in under the tax free threshold for that financial year.
However, the income on my child support assessment included that redundancy payment.
Once she gets her tax done it will filter out and if you have overpaid she will need to repay you or it will be considered credit.
She can say what she likes but it will filter out when she gets her tax done, she can't hide the payment.