sorry for your loss
are you the administrator of his estate. then file Form 56 with the IRS
https://www.irs.gov/pub/irs-pdf/f56.pdf
without the form, the IRS will not release any info to you. so that would mean all you can do is ask her.
if she filed after his death, under the tax laws she should have included form 1310 with box C in part 1 checked. Part II would need to be completed.
https://www.irs.gov/pub/irs-pdf/f1310.pdf
if she filed after he died but didn't indicate this on the return, the IRS would not know the need for the form.
this is question 3 in part II
As the person claiming the refund for the decedent’s estate, will you pay out the refund according to the laws
of the state where the decedent was a legal resident? . . . . . . . . . . . . . . . . . . . Yes or No
If you answered “No” to 3, a refund cannot be made until you submit a court certificate showing your appointment as the personal representative or other evidence that you are entitled under state law to receive the refund.
since we don't know exactly what happened, this may become an issue for a lawyer.
for example, direct deposit into the joint a/c was specified on the tax return and it was filed while he was alive. In this situation, I don't think the IRS is going to be of any help.
even after filing form 56, you may find it difficult to get hold of the IRS.
