CityGal,

From your description I assume your therapist is using a single channel TENS (transcutaneous electrical nerve stimulation) or other e-stim device - for what reason I am unsure. If you have pain and swelling in the midfoot then I would deem it an appropriate symptomatic modality; if not then I don't see the point.

As for whether this treatment could account for the new medial ankle pain I think it would be unlikely to be a direct cause and effect. Perhaps they have given you some other exercises/stretches for the ankle/foot that may be more relevant to this pain e.g. heel raises, ankle pumps in hamstring stretch position etc. A number of structures can generate pain in that area - more symptom and therapy information is needed to answer your question more thoroughly.

Hope this helps a little.