retiredtraveler...You and your friend are not alone. I have been suffering for a year with this condition...and still struggle with the pain. Treatment is pretty standard...heat, ice, stretch, anti-inflammatories. I went to physical therapy for 3 weeks as the condition worsened and I developed sciatica as well. The doctor said this is a common condition for runners and athletes. Guess it isn't just for us old folks...take care.
Obviously as you age you potentially have problems with your feet. I have had TKRs on both knees, followed by plantar faciata in my left foot. Likely this was brought on by walking incorrectly prior to surgery. The treatments are not guaranteed, but I have found the stretching exercises work the best. There are various ones you can find on line - the most important one is where you cross your legs at knees, grab your big toe and pull it up and towards your face. This directly stretches the primary ligament that causes PF. It takes time and it will hurt at first.
In addition, you must exercise - aerobic and anerobic. You must strengthen your legs, thighs, calves, buttocks, ankels, etc. The best way to do this is weight machines. The stronger you make your legs the less problems you will have with issues like PF. If you are in very bad condition, you may want to start with a sport physical therapist - which Medicare will cover with a Dr perscription.
Then you must walk, once the PF has subsided. My understanding is that PF is really a form of inflamation of specific muscles and ligaments. So you need to treat the inflamation first then exercise and stretch like there is no tomorrow.