Craft 2: Suspend user results in "Unauthorized You don’t have the proper credentials to access this page."
Is she trying to suspend another user who's an admin user?
I just tested this and your scenario would happen if she's trying to suspend an Admin's account.
A user who's has Admin privileges can only suspend another Admin otherwise you'd have users with lower-level permissions overriding those with higher level ones.
In Craft 3, you get a more clear message if this happens: