I can't think of any setting offhand that would prevent it, but I do have a suggestion that might make things a little easier on the user and could possible get around the issue with this particular user's computer.
Try putting this in the double click Event of whatever fields you want to zoom:
DoCmd.RunCommand acCmdZoomBox
This way all they have to do is Double Click to get the Zoom Box. It's a little easier to do than SHIFT+F2. You may even prefer it in another event, it's up to you.
HTH, Thanks.