The most visible peds on my commute are the ones who carry the light in their hand because it makes it move up and down and all around while they are moving. You can sell that as an enhanced workout with weights in each hand.

If she's a weight weenie, than tell her to leave off the pullover when the vest goes on, its a fair trade.

If she persists and she's also one of those joggers who runs in the roadway facing oncoming traffic, perhaps setup an interaction with a ninja cyclist coming at her in the dark, who skids the last couple meters and screams at her to get off the road, and hope she doesn't get hit.