IVRs and receptionists

I’m wondering if there’s a straight-forward way to do the following…

We have a virtual office situation at our non-profit where everybody works from home. We’d like to be able to make it so that when our administrative assistant is logged in via her softphone/ipphone/etc (or something other than time specific since it changes regularly) that all incoming calls are rung at her extension in order to add a personal touch. Then any other time (when she’s not logged in) they go right the IVR.

Is that doable?..try as I might to think of a way…nothing is coming to me.

Since I’m new to all this and don’t know if it matters…I’m running FreePBX and asterisk 1.4 on a pbxiaf install.

Could you not just direct all calls to her exten with failover to the IVR in the IVR make a selection to leave voice mail for the administrative assistant
and send it to her voicemail.

does that not give you want you want???