Soaking is okay with frostbite, just no scrubbing or massaging. It looks to me more like a smash injury, or a frostbitten foot that has been injured (if only one foot got wet.) She might have gotten the foot stuck under something as well. To be honest, I use a heat lamp in zero temperatures, just to slightly warm the area under it, but it is secured twice, bulb is tightened and checked daily.