What a lovely idea! You can make an easy salt scrub with either epsom salt or kosher salt (or a combo of the two) and a light oil like almond oil. Use a 2:1 ration salt to oil. Adding tto or peppermint oil would give a nice cooling effect. Dried orange or lemon peel make a nice scrub too. Remove the colored part of the peel (the zest) with a zester or sharp paring knife. Dry the peels thoroughly by either laying on a rack to air dry near a sunny window or you can place on a cookie sheet in a 150 degree oven for several hours...or if you have an electric food dehydrator, just follow the manufacturer's directions. Once the peels are completely dry coarsley grind them in a blender or coffee grinder until they are the consistency of coffee grounds or cornmeal. Place the ground peels in a clean bowl and allow to air dry further if they are not completely dry. Use the ground peels imixed in equal amounts with water, your favorite cream or soap....plain yogurt is nice too. You can add oatmeal or cornmeal for extra scrubbing power.
For an invigorating foot rub mix together 2 Tbs. light oil, 1/2 tsp. vinegar, 1/2 tsp alum powder, 1/4 tsp camphor oil. The vinegar and camphor are mildly astringent and cooling and will stimulate and energize her swollen feet and ankles.
What a great friend! Have fun!