"she should submit a new W-9 with all same info listed above EXCEPT the S Corp box should be checked (not the individual/SP/single member LLC box)?"

None of the Above. You mark that it is an S Corp, and an S Corp is Exempt from 1099-NEC reporting. You enter the Corporate name and FEIN.

Box 1 Corp.

Box 3 LLC as S Corp.

That's part of why I commented: need to understand what "operating as an S Corp" means, include how to properly sign papers, payroll, etc.

"I question if that is possible given he recommended it in October 2021 for 2021 income"

Do some due diligence; ask for the IRS letter accepting that there is an S Corp, and the document showing there was an FEIN issued.

Who has been running payroll for this person's corporation since 2021? And if that wasn't even formed until Oct, was it applied for retroactively, or is the first 3/4 of 2021 not as the S Corp?