Why is anybody talking to an "agent" about this?
An "agent" sells the policy on a local level.
He is not the claims department which is typically located at the insurance company's home office.
The beneficiary that's named on the policy should be dealing with the home office claims department and not the local "agent."
The policy itself should have the location of the home office and a toll free number for the claims department or you can look up all you need to know about the insurance company on the A. M. Best website:
Once the beneficiary gets a claim opened with the right claim rep, the claim rep ought to be able to help piece together the information needed to settle the claim.
Keep in mind, though, that properly identifying the deceased is critical and if your sister messed things up it's not going to happen overnight.
If you continue to have problems, contact the Tennessee Department of Insurance for assistance.