You could go to the Greetings menu of the subscriber and set a blank recording (or she can record a greeting) and then change the After Greeting option to send the caller to another person, another call handler or just to Hang Up.
She could do all that under her Alternate Greeting and turn on her greeting while she's out.
You can also turn on the extended abscence greeting in recent versions of Unity (4.0(5) or later). One of the options is to not take messages while the alternate greeting is active - when the user dials in to check messages they can also be warned about the fact that their alternate greeting is active so they don't forget to turn it off when they return from leave.
I'm not able to access my old voice mail messages all of a sudden. The recording says something like 'the message is currently not available'. This has never happened before in all the years I have been using this system. I have t...