(I am positive its not plantar fasciitis as she has no post static dyskinesia and the pain doesn't warm up as she walks)
Be a little careful here- an atypical presentation of a common pathology is more likely an an atypical pathology...
You have 2 parts to the problem-
What is the actual diagnosis, and what is the cause.
Sometimes with PF it can be hypersensitive and irritable so that nothing short of complete offloading will allow it to settle. In this case you may end up putting her in a walking boot or similar.
I would be interested in knowing how she responded to your other management such as the stretching and footwear change.
Some more information with respect to the history may help- did it start initially with morning pain and has progressed since that time (many do not seek treatment until it has progressed)?
How was the original onset? Sudden? After a long day on her feet? etc etc...
My suspicion from your information would be that she needs to have the pain settled somewhat before you could reasonably assess and address biomechanics.
Consider other things such as trigger points and calcaneal oedema...
I hope these quick thoughts help.