Hi and welcome to the MS community although what your dealing with is not specifically an MS issue, people with MS can and do still experience Plantar Fasciitis and Heel Spurs just like anybody.
It's possible with plantar fasciitis and heel spurs to additionally experience compensatory ankle issues basically because the ankle joint has to do a lot more work to keep the ankle stable and it can cause pain or discomfort that runs down either side of the ankle bone.
One of the more common causes of plantar fasciitis and heel spurs, as well as ankle issues, is not actually a problem with the feet or ankle but from overly tight calf muscles, which is why calf stretching is typically part of the treatment plan.
"Exercise. Plantar fasciitis is aggravated by tight muscles in your feet and calves. Stretching your calves and plantar fascia is the most effective way to relieve the pain that comes with this condition.
Lean forward against a wall with one knee straight and the heel on the ground. Place the other leg in front, with the knee bent. To stretch the calf muscles and the heel cord, push your hips toward the wall in a controlled fashion. Hold the position for 10 seconds and relax. Repeat this exercise 20 times for each foot. A strong pull in the calf should be felt during the stretch.
Plantar fascia stretch
This stretch is performed in the seated position. Cross your affected foot over the knee of your other leg. Grasp the toes of your painful foot and slowly pull them toward you in a controlled fashion. If it is difficult to reach your foot, wrap a towel around your big toe to help pull your toes toward you. Place your other hand along the plantar fascia. The fascia should feel like a tight band along the bottom of your foot when stretched. Hold the stretch for 10 seconds. Repeat it 20 times for each foot. This exercise is best done in the morning before standing or walking."
I'd recommend you consult your dr and consider seeing a physio.
Hope that helps......JJ