Spouse of a deceased non-vested employee with contributions in DB Retirement Plan wants to roll those contributions to an IRA so that taxes will not have to be paid. However, our bank that sends out the pension payments automatically takes 20% in taxes on distributions. If the spouse receives the money minus 20% for taxes, can she put the money into her IRA anyway and take a tax credit on the 20% that was taken out for taxes?

There may be some confusing terminology here: "Contributions in DB plan".
If this means that the deceased made contributions to the plan, typically by payroll deduction, then the next question is whether those were pre-tax or after-tax contributions. In the U.S., the only such pre-tax contributions possible are in a governmental plan. All other sponsors (whether non-profit or for-profit) could permit employee contributions only on an after-tax basis to a DB plan. (At least I hope that is right.) Such plans are generally rare.

After-tax contributions are not eligible for rollover to an IRA, and would also not be subject to any (20% or otherwise) withholding. There would likely be some interest to be paid, which is taxable and (I think) rollable.

Did I miss anything?