I believe there is two major factors here : the first one, as you stated, is to hit a few fast food places along the way.Why is she travelling so far from home for like 2 minutes of walk that's already making her struggle? At her current weight she could just go on a walk around her block or something. (...) I have a feeling this is just an excuse to eat out. "Oh, I was away from home, travelling. Of course I had to stop for something to eat at a fast food chain, nothing else to find."
The second one is because she doesn't want to be seen. Notice how she always w̶a̶d̶d̶l̶e̶ walk in a remote places where there is not a single other person? Chantal hides. Even as a narcissist, deep down under all the lard she knows she looks like a fucking freak show. Imagine crossing path with a +400lbs red faced behemoth sporting a cheap Versace knockoff t-shirt and sunglasses even Elton John himself would be ashamed of, huffing and puffing after 10 meters?
Freak show material right here. If we looked like Chantal we would, too, go far from civilisation to walk our weekly 100 steps.