You should pursue the question of why your mother has low blood potassium with her physician. The conditions noted above are potentially correctible, and detection of the nature of the problem should not be too difficult. About 2-6 grams of potassium are supplied daily in the typical American diet. Potassium supplements that you can buy in the drugstore without a prescription contain 99 milligrams of potassium in each tablet. Also, a multivitamin may also serve as a good supplement for your mother's diet.
Many salt substitutes provide potassium as well - check the label.
We hope this information will be helpful to you and your mother.