Sounds like sundowning in humans, where dementia symptoms get worse at night. If you think she would fare better being confined, even crated at night, then I wouldn’t worry about whether it’s “fair”. She has special needs now and may need different treatment than the others, and being crated at night may make her feel more secure if she is confused and anxious, especially if she’s always seen it as her safe zone. If it would be more stressful on her though, that’s something else.
Have you talked to your vet about this? I’ve never personally had a dog with dementia, but I know there is a medication that can be used to treat it (anipryl?). Also some people have seen success with Pro-Plan’s new Bright Minds formula, although again, I don’t have personal experience.