Letter of Testamentary

In some states this may be referred to as a "Short Certificate." It is literally like a few lines, with a seal from the county.

Agreeing with RedHobbs, it's basically the county approving you, that the will that you have is the one going on record for everything with the estate moving forward. This way the bank knows that you didn't just type it up, forge a signature and a notary stamp, as boomhaeur mentioned above.

You will also want to go back with a death certificate. Typically they will cross reference the surviving spouse name on the death certificate with the name on the will and the ID of your grandmother as another method to make sure everything "makes sense."

Even though the $200 seems like a lot of money for a small savings account, remember that it also protects your grandmother as the executrix. So if any one tries to do anything on this behalf with a fake will (you'd be surprised how many families do crazy things when someone dies or in cases of fraud) you will have the proof from the county your copy is true. It may also be required in cases of real estate such as removing his name from the title of her home (if she wants to sell or gift the home later, she will need proof he passed away in order to sell the property if he was a joint owner). If he has other accounts, retirement funds that your grandmother will inherit, real estate, life insurance, trusts, cars, social security, incoming dividend checks, etc, it may be required for those as well. And it will also protect and assist your grandmothers executor as well, in a case that god forbid, she passes away before her husband's estate is closed (more likely in cases where an estate is open for several years).

A notary or affidavit will not help in your case because it needs to be on record with the county.

That being said, some larger banks will allow access to a limited amount of funds to an immediate family member or funeral director without those documents, who can prove that the funds will be used to cover the cost of final expenses. But in that case, you will have to provide a receipt or bill from a funeral home accompanied by a letter from the funeral director. You would want to contact the bank first (try contacting their hotline instead of the same employee who assisted you) before attempting this approach since it requires more paperwork, and depends on the bank and the state you reside in.

I hope this helps. Good luck <3

Source: Banker, notary for 5+ years.