Well “actual pixels” is a bit relative to your screen size and resolution, so holding up the actual object to your screen will be slightly off.
Just turn on the ruler in PS and compare its measurement of the template to the size of the actual insert.

 Or why don’t you make it easier on yourself and especially your technically challenged sister (I’ve got one of those, so I know), and just download one of the hundreds of free/trial jewel case label software.
If you already have a 3rd party burning software like Nero they come with one.

 Do your cover design in PS, open the label maker software and just insert it, then save as a Pdf.
Note: If you send a technically challenged sister anything other than a Word or Acrobat Reader document, they are totally lost (Trust Me!).

Chuck