Sorry, I did have a moment... You Mom has shingles and then A UTI and dehydration. It's late
Please forgive me!
If the doctor's didn't mention any heart problems but there was UTI and dehydration then there could be a connection to the kidneys. I showed doctor's and nurses my Mom's swollen ankles for years... then one day they just cleared up. I am sure it was because of her consistent walking. I do know that many of our residents develop swelling when they sit too much. Just as we do on a long plane ride. Be sure she is up some and down some and her feet propped up some. Position changes are the best thing to try first.
Cellulitis is possible so be sure to check for heat, redness, and skin breakdown. It never hurts to have a doctor check her out