...a simple suggestion, from a simple person (me). Your friend seems to be one of those people who has not made the mental leap to exercise routines needing to be part of your daily life. Thus, her bike comes to work on top of the car, while your bike rides to work as part of your routine. I have, myself, attempted to nudge people in the direction of bicycle commuting, because it works some regular exercise into your routine, and usually ends up taking not that much longer than driving, by the time your fight traffic and park. Sometimes it works, until the weather gets bad. I realize you live in a smaller town, and it's entirely possible she needs to drop kids at day care or school.
But if that's the case, she's not well situated to use a bike as a valuable part of a regular exercise routine. Life is short, and there are only so many hours in the day. I would offer to sit and talk with her, looking at her weekly schedule, and try to figure out some portion of the week she could use to work in exercise as part of her routine. It might even be a stop at the gym on her way home, or several evenings weekly when her partner takes care of the kids.
Nobody is gonna lose massive amounts of weight and get whipped into shape riding their bike during lunch, at work. It's just not realistic.