The access level needed by your office manager really depends on how you have your access level requirements set up and what functions you want your OM to complete. The access levels and ability to track those functions are set in File>Security>Edit access levels.
In here it lists the Event Type (part of program), Event (specific function), Required Level and Write to Log information.
These required levels are customizable to meet your needs.
Once you've set these access levels up, it's a matter of corresponding your OM access level to allow needed tasks to be completed.
The Write to Log column gives four options.
1.) Always - Anytime this event is completed or attempted it will be tracked in main security log.
2.) Never - Just as it says, it will not track this event at all
3.) On-Success - If someone attempts and completes the event successfully.
4.) On-Failure - If someone attempts to complete an event, but does not have the access level needed to complete it.
I hope this information proves helpful to you.
Just to tag onto Robert's post.... Unless settings have changed, some tasks are labeled as "viewed/edited" and you cannot tell if the employee simply viewed OR if they actually edited something. I requested years ago that these be two separate log entries, but again, not sure if it has changed.