We need to file an amendment to a SAR due to an error the filer made in item 24 Relationship of subject to institution. I have updated the original narrative with a beginning sentence explaining the amendment and correction. My question is, when I file the amendment should I attached the spreadsheet that was included in the original filing?

I've not seen anything affirmatively address spreadsheets specifically, but this is from FinCEN's SAR FAQs:
"The filer should complete the FinCEN SAR in its entirety, including the corrected/amended information and noting those corrections at the beginning of the narrative, save (and print, if desired) a copy of the filing, and submit the filing."

Yes and in my mind that would include attaching the spreadsheet, but our internal audit says it does not.

Are they saying it is a problem to include the spreadsheet? Do they have a citation?

If you leave off the spreadsheet, then it will no longer show in the amended record I believe. As Adam said, the spreadsheet is part of the SAR "in its entirety". It totally replaces the original.