The nylon/cotton will not pose a problem, just keep it as thin as you reasonably can to get the coils as close to the skin as possible.
It might help to use coil pairs instead of a pad. You will get MUCH more effective penetration if you use a single pair of stacked coils (bumpy-side-to-bumpy-side, taped together). Place directly over the point of pain, or over the center of the pain if it is a larger area.
Even better, consider try placing coils on opposite sides (top and bottom of the foot), with bumpy side of each coil away from the skin.
If you decide to try either (or both) of those, keep at it every day for at least 2-3 weeks, 6-8 hours per day. Then let us know how it worked for her.
The key thing is not to try to treat every spot simultaneously. Choose the most painful or original spot where the pain first appeared. If you treat this thoroughly, pain in other locations tends to be reduced.
The theory behind this is that the original injury acts as a pro-inflammatroy signal “beacon” that causes inflammation in other locations secondarily, and if you can quench the signal from this original pro-inflammatory source, you benefit because this signal is no longer driving pathologic inflammation throughout the body and causing problems elsewhere.
One thing to watch out for is that when you employ this strategy, when the original source of pain is reduced, all of a sudden then all other locations of lesser pain feel much worse (more pain). This is a sensory illusion, explained by the theory of lateral inhibition of sensory neurons in the cortex. Briefly, your brain tends to focus on the one largest pain signal, and it does so by dialing down adjacent pain signals. So, when the main signal is reduced, the other pain signals get dialed back up and you get the illusion of more pain.
Sometimes people will tend to panic, thinking “oh my god, now its worse all over, what have I done!!!???” Then they either quit abruptly or they try to chase around the many different points of pain throughout their body with coils. The many of them demand that I build a whole-body machine.
But that is not the most effective strategy, and the sensory illusion of “more pain” is temporary. The best strategy is to understand this illusion, and just keep treating the original source of pain until it is completely recovered and the cortex has had a chance to re-equilibrate to sense the pain signals correctly. If you stick to this strategy, the effect (about 90% of the time) is that first the main source of pain and inflammation will subside, then many or all other locations of pain will also tend to fade away.