Of course, not everyone appreciates the informality of email. You may want to call the gatekeeper. Before doing so, role play your pitch with a friend. Ask your friend to play the most difficult scenarios, including that of the over-protective secretary. To get past the secretary, try calling before or after work hours.
People often answer their own phone when they stay late.
You may get lucky, she may assume that she should know you, after all, you know her, and she may connect you. If you are refused, you may want to ask the secretary if she will put you through to the gatekeeper's voice mail. If she will, use that forum to make your personal pitch.