This treatment is being suggested on bases of the information provided. However I would like to examine & investigate your  mother in detail. -Control  Hypertension, Diabetes or  metabolic disorder, if there is any. --. Sleep on a hard bed with soft bedding. --. Keep a pillow under the foot. --. Avoid painful acts & activities. --. Fomentation with warm water. Let the part not be exposed to cold. -- .Do mild exercises for the affected part.- foot and ankles. --.(Take help of physiotherapist or you can visit my YouTube channel Dr. N. C. Gupta and watch 'Me & My Yoga' and 'Yoga Simplified'. https://youtube.com/channel/UCPEQc6B1ywzwin048JSu6rw --Do not ignore, let it not become beginning of a major problem. -Any way it may be tried, --. Ugesic (Piroxicam) 20mg 1 tab od x 5days --. Caldikind plus  (Mankind) 1 tab OD x 10 days. -(You may need help of your local doctor to get these medicines.) --Do ask for a detailed treatment plan. Kindly make sure, there is no allergy to any of these medicines. --For emergency treatment visit nearest hospital. --Wish your  mother a quick recovery & good health.  Dr N C Gupta MS (ortho)

It may be planter fasciitis, retrocalcaneal burstis or mortans metatarsalgia. The way she is feeling pain you are telling most probably she is suffering from planter fasciitis. If it is then sleeper modification hot and cold fomentation and a pain killers is treatment options.

Many reason for pain . She need to get examined and evaluated then only treatment start .