I have not heard of vertigo as a symptom of Alzheimer's disease(AD). The AD folks I have known, who have shown signs of lighthead or dizziness, have found answers in
further medical workups which revealed such treatable issues as inner ear infection or wax buildup, allergies, visual changes, metabolic disturbances such as high blood pressure, and environmental causes. This latter may be of great importance in finding the appropriate way to deal with this uncomfortable symptom. For instance, shiny floors, glass coverings on pictures, sounds or smells in the area around her, shadows cast by household furnishings or from outside a window are some of the environmental issues that professional and trained caregivers often assess when vertigo arises. Since the senses seem to be affected by Alzheimer's, it is not uncommon for AD folk to have difficulty functioning in a space that may not be Alzheimer-friendly. If you can find the environmental culprit, including the time of day and room or area where it occurs, you may be able to change the instances of dizziness by addressing necessary changes in the environment.
Occasionally, the AD person is not able to correctly articulate where or what physical changes may be happening and that compounds finding the proper treatments. My husband, while in the mid-stage of a dementing illness, once complained for hours about a headache. In fact, he had a stomach ulcer and his head was not affected at all. Even though he was clearly telling me of severe discomfort, his inability to relate the place of his pain was a result of the neurological disease.
Above all else, do keep the physician appraised of your mother's problem and do take care of YOU!