Outlook calendar issue

Hi everyone. I have a user that's having an issue with the Outlook calendar and being able to see meetings on other people's calendars. This person might open up 8 or 10 people's calendars at a time in Outlook 2007. Here's what she's experiencing. After sending a meeting request to some users it will show up on some users calendars without their having accepted it and not on others. This is evident when she view everyone's calendars in her Outlook. And sometimes when someone has accepted a meeting she'll get the response back that they accepted it but she doesn't see it on their calendar (when she's viewing their calendar in her Outlook). I'm pretty sure she has at least view or reviewer access to all of these users calendars. Could the problem be as simple as not having reviewer access on everyone's calendars?