Client in FL Nursing Home, Son in IL

Have a client who lives in Illinois. He and his brother are POA for their mother, who moved to a nursing home in 2019 in FL where she's been a resident for many years.

For 2019 to now, I've been filing Mother's return using 'in care of' her son and his Illinois address. Now IL has sent notices for all three years demanding resident taxes. Of course he can prove that she's a Florida resident, but what can I do, besides filing an Illinois return for her to prevent these notices. I do file a non resident Oklahoma return for her because she has Schedule E Royalties income for that state (which is what IL wants taxes on).

Respond to the notices with an explanation of the situation.

Respond to the notices with an explanation of the situation.

That's plan one but what can I do to stop future notices? Especially since I plan to retire next year?

If explaining the situation to the IL DOR doesn't work in the long-term, I might suggest the son open a virtual mailbox in FL and use that as the address for his mother's tax reporting.

Another option is to file a zero nonresident IL return each year, however I'm not certain that will stop the notices. Presumably a 1099 is being issued for the royalties with a IL address for the mom, and this is why IL thinks it's IL resident income.

The IRS sent IL the info though the IL address is on the 1099.

Virtual mailbox? Great suggestion. Thanks.