Is the IRA that she gets $6k from annually Roth or traditional?
Assuming that it is traditional, I'm only coming up with $46,800 that is subject to ordinary income taxes (dividends are taxed separately).
Income: $90,000
RMDs: 6,000
Less:
457/403b: (39,000)
Insurance: (4,800)
Pension: (5,400)
Total: $46,800
2020 Std deduction: $24,800
Subject to ordinary tax: $22,000
So, you could convert up to $58,250 and still keep everything within the 12% bracket. Obviously, it'll change each year as tax brackets and the standard deduction shift with inflation, but that's a good ballpark (and not being exact won't hurt that much).
@Cpa Cat @seattlecyclone are the tax people (IIRC), so they might be able to give better answers than me.