Before she pays a dime, have her check into it and make sure the number they gave her is accurate. Since she is a medically retired Firefighter, have her talk with her union rep and get them involved. They would be the ones who set up the pension/insurance payments and they should have the answers she needs. They should also be able to help her with the IRS.
We got a letter once telling us we owed thousands in back taxes & we disputed it. Turns out the IRS made a mistake!! Yes, it can happen & yes, they admitted it. We ended up only owing a few hundrerd dollars - a HUGE difference from the original amount in the letter.
If she does owe the larger sum, then the IRS should agree to a payment schedule - it is usually in the letter, but if not call and talk to a "real" person, not the automated system.
Good-Luck !~ B.