Welcome to the site. I'mCustomer and will be helping you today. While I'm not a bankruptcy attorney, I can assist.
Trustees have been charged with obtaining all they can from a bankruptcy estate. In a car like yours, v they often make a claim for what I call the trailing refund, explicitly if your wife did not have any remaining cash exemptions.
The trustee action is a threat, that he hopes will get you to release some money. Your offer of half was not enough.
He can reopen the bankruptcy, since the refund was joint and for the year the estate was closed (the bankruptcy estate includes that refund).
I would consider the cost of not giving up the refund and having to go back to court, including legal, loss of work, and the aggravation.
I would consider amending your joint tax filing
to see if you could segregate your wife's income
and the bankruptcy estate. It is possible to split her tax year into the bankruptcy estate and the remainder of the short year. This might segregate your joint tax year and isolate it from trustee pursuit.
This technique is perfectly legit, and different bankruptcy districts will test the post- estate return differently. You should consult a tax pro in your area to see if this technique will work in your area.
Thanks for asking at just answer. Positive feedback is appreciated. I'mCustomer