Mail pdf refuses to be icon

The default behavior for a 1-page PDF attachment is the full-page view. You right-click on that PDF and choose the menu item View as Icon from the secondary menu. There is no means to change this default Apple Mail behavior when attaching a single-page PDF, unless you want to zip compress that PDF and attach that .zip container, which would not endear you to the recipient.

Either compress the 1 page PDF file or put it in a folder and then add to the email. But setting it as an icon is only for your computer. You have no control (other than the compression and folder methods) on how the pdf is handled by the recipient. That will be unique to their computer.

Or you can add a blank page to the PDF and that will let you view it as an icon.

Tell her to create a single page PDF with just these words on it:

This page intentionally left blank

Then she can add the pdf page to any other pdf as needed. 😉

I attached a single-page PDF to Apple Mail in Monterey 12.6. I have View as Icon on a secondary menu from a right-click. Why you do not is a mystery.