|I will agree that it is tough to enforce a policy that seems so easy to break.|
It would be in my opinion a better policy to access the router and setup access times. Then tell the employee that she will only be allowed access between this time and that time to do personal business.
I have stated before how dangerous it is to allow internet on a business computer. I'd disable it completely and put a junky computer in the corner to access only internet.
There is no business reason to lie to her.
"Best Practices", Event viewer, host file, perfmon, antivirus, anti-spyware, Live CD's, backups, are in my top 10