I am sorry your mother is not able to get her dementia medication. I don't have specific advice about what Medicaid will or will not cover; you would have to address that with them.
If you are in the US you can call the Alzheimer's Association at 1-800-272-3900. That number is answered 24/7.
Your local Council on Aging (usually through the state or county in which you live) may also be able to help you. For instance, Google "Boston MA Council Aging" or wherever you live, and you should find results. Sometimes it's called "Aging Services" or "Department of Senior Services."
That's where I would begin. If your mother receives any sort of social services (from a residential care home, a social worker, a local agency) you might ask them also, as well as her primary care physician.