We are being audited to IATF 16949. I'm just trying to get my mind wrapped around where she is coming from. Any help would be most welcome.
Since you're being audited to IATF 16949, let's look at what it requires for MSA:
Statistical studies shall be conducted to analyze the variation present in the results of each type of inspection, measurement, and test equipment system identified in the control plan. The analytical methods and acceptance criteria used shall conform to those in reference manuals on measurement systems analysis. Other analytical methods and acceptance criteria may be used if approved by the customer.
Records of customer acceptance of alternative methods shall be retained along with results from alternative measurement system analysis (see Section 126.96.36.199).
Note Prioritization of MSA studies should focus on critical or special product or process characteristics.
I don't see anything in there that requires Cp/Cpk for gage studies. It says you analyze the variation in the gage systems but doesn't specify how.
Let's look a the AIAG MSA Manual. Here's the stated purpose in the manual:
The purpose of this document is to present guidelines for assessing the quality of a measurement system. Although the guidelines are general enough to be used for any measurement system, they are intended primarily for the measurement systems used in the industrial world. This document is not intended to be a compendium of analyses for all measurement systems. Its primary focus is measurement systems where the readings can be replicated on each part. Many of the analyses are useful with other types of measurement systems and the manual does contain references and suggestions. It is recommended that competent statistical resources be consulted for more complex or unusual situations not discussed here. Customer approval is required for measurement systems analysis methods not covered in this manual.
First, the MSA manual is a guidance document, not a requirements document. Second, if you read the entire manual (I have) you'll find that using Cp/Cpk for gage studies is not covered in the manual and per the last sentence in the quote you would need to have customer approval to even use that method. Unless you have a customer-specific requirement that specifies that method, I don't see where they are coming from.
The short story is that the auditor is trying to write a nonconformity to a requirement that doesn't exist. The ISO definition of nonconformity is "non-fulfillment of a requirement." The auditor must specify a requirement if they write a nonconformity, which is why I asked what they quoted as the requirement. My guess is that they haven't quoted one.
You didn't mention what kind of audit this is. If it's a certification body audit my suggestion is that you appeal the finding with the certification body. Every certification body is required to have an appeals process using personnel independent from the auditor. Findings like this is what it's for. If the auditor is still there, please ask them to show you where the requirement is and I suspect that the NC will magically disappear.