the physics of bushfires, page-8

She is wrong Yak. Simply, a bushfire thrives on the "pre-heat" factor -a driving wind (and hot air temperatures) as well as the flames themselves help preheat whatever is in the path of the flames, facilitating its ignition & combustion.
Without even considering the laws of physics, one can visualise how flames approaching a hillside would preheat up the slope much more efficiently than on the flat. Going downhill would actually have a retarding effect.

Cheers
GZ