I have dealt with several different types of non-profits. First, you need to read IRS requests to determine what is necessary for you to respond. If you then decide to take on the project, immediately respond to IRS stating you will be working on their case, and request an extension of time to complete--depending on your assessment of how long it will take you to arrive at the correct information needed to satisfy IRS needs. Generally they will grant it--I would go for at least 45-60 days (guessing blind). You do not have to have an POA signed unless you really want to be in the middle of whatever it is IRS needs. You can complete info without discussing with IRS, until or after you have submitted your completed work to them. At which time, should you then desire a POA, at least by then you know what you have before you. I don't know what state you are in, but beware there may be state requirements to fulfill also.
Daune/CA