Very very sad to read this and hope that a recovery is possible in time. While I am not in the same situation, my 79 year old mother is getting tested for what I assume may be early dementia and its absolutely terrifying to have anything happen to your mom...
Before assuming its dementia please be aware that "dementia-like" symptoms are exhibited by elderly people with UTIs. My mum was 85 and suddenly "declined". I asked GP for antibiotics and said to him could we just assume its an UTI and try that and suddenly she "recovered". (Unfortunately she died for other reasons a few months later)
Dont give up hope!