Mother has dementia, where do I start?

Remember, dementia is not a disease. It refers to certain symptoms caused by some underlying issue. It may or may not be treatable. The testing should indicate the cause of the dementia. Dementia can have as many as 70 different causes. Unfortunately, Alzheimer's is the leading cause of dementia. If the tests indicate a progressive neurodegenerative disease like AD, the best thing you can do is to become educated about the disease. There are some excellent books on the subject of dementia and AD. "The 36 Hour Day", and "Learning to speak Alzheimer's" are two. Also, Teepa Snow has over 100 videos about the subject. Go to YouTube and search for "Teepa Snow".

The first thing I recommend doing is to listen to this video series by Teepa Snow, a dementia expert:

https://www.youtube.com/playlist?list=PLVl8vTLjje8ESAEvpjVoVTEK-_6X2jTdl