Well you should probably contact your local department for welfare for older people, which is a social services department. They can do an assessment of your mother and between you decide on the type of care she needs. If your mother's demetia is mild, then being in the type of unit she's in can only serve to make her worse, as she probably is getting no mental stimulation.
My elderly mother is quite frail, has Diabetes, heart problems and can has poor short term memory, but hasn't been diagnosed with Dementia. She lives alone, but has a care package, where she is visited 3 times per day by carers, who wash and dress her, make her breakfast and lunch and then come back in the evening to settle her. I'm not sure that this kind of care would suit your mother, but there are many options available.
At the moment I'm trying to arrange for her to attend a daycare centre, although she has regular visiters, she's getting little stimulation, as she can't go out alone anymore.