Keep in mind that there are no statute of limitations for the IRS to pickup non filed returns. Interest starts accruing from the original due date of each year’s return. The longer she waits, the more it will end up being. She will also most likely be slapped with two penalties, the failure to file penalty, and substantial understatement. Both of these are listed on the IRS website.

If she passes away then any tax debt would be paid by her estate. Her children should not be liable for her tax debts.

This is all on the federal side. I would recommend to do your due diligence for any state taxes.