I am so sorry to hear you are worried about Regis. I am a veterinarian and will do my best to help.
When a dog stops eating, it is a sign of illness or suffering. If I have diagnosed a dog with a serious illness, like cancer, and the dog's owners want to know when she is suffering, or when it is time for humane euthanasia, I tell them that when she stops eating, that is when it is time.
Emaciation is a sign of pain, chronic illness, cancer.
A dog with a serious or fatal illness will first stop eating their dry food, gradually eating less and less, until they get to eating only the one or two things they really like. Then, they stop eating even those.
The aimless wandering could be senility, mental confusion/brain
tumor, or pain/trying to get comfortable.
I would consider having her examined, to find out if what is causing her to stop eating is treatable at all. She may improve with pain medication, appetite stimulants, or need specific treatment for a specific condition. It might be time to consider humane euthanasia.
Keep offering her things she likes, baby food, soup, broth, her favorite foods until you can have an exam and consult with a veterinarian.
Let me know what else I can help with or answer. I am sorry you are worried about her condition, and she does sound very ill.