Nothing to be concerned about if she has no other problem.
However, if you or she are bothered by this behavior anyway, you can consider the following ideas if you want to be thorough or if you think someone (she or someone else to had access to her Mac) may have added some software to her computer:
(1) If your GF added software that uses the camera automatically, you can follow the developer's instructions to disable or even uninstall it.
(2) Look in your GF's Login or startup items for items that may be using the camera automatically. If you find any, delete them from this list to stop it from running automatically.
You don't say which specific Mac OS X version (10.3.9, 10.4.11, 10.7.3, etc.) she uses, so I cannot give exact terminology. In Lion, you will find this in the > System Preferences... > Users & Groups item.
Earlier OS X versions called it > System Preferences... > Accounts. In any OS X version, clicking on the iCon showing the silhouette of two people as shown here is where you look.
(3) Check for widgets that may be using your GF's iSight. You can delete any you find that you do not want to keep. Restart your Mac when done and the widget will be gone from her system.
(4) If the light continues illuminate periodically, and if she is bothered by it,
Apple's iSight Troubleshooting suggestions are the next thing to try.
Be sure to check more than one Apple camera-enabled app in more than one user account. However, if your GF's OS X version has one, don't use the "Guest" account for testing. If her Mac only has one user account, create a new one for testing.
If the problem remains in all user accounts you test, the proper "reset" suggested in the troubleshooting article for her particular Mac model can sometimes restores normal iSight function. Otherwise, there may be a hardware problem that will require the services of an Apple Authorized Service Provider.