Sleep deprivation and sleep disorders can impact our health in a major way. Cognitive ability can be impacted and yes, I'm sure headaches can be triggered. I had not heard about a correlation with alzheimers. In reading about that, it's a little confusing. I guess many with alzheimers do have disturbed circadian rhythm. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4351409/ I don't know if it causes it but is more just part of it though. Has your aunt been diagnosed with Alzheimer's?
I have issues with this myself a bit as it is also common for women with hormonal changes going through menopause. Good times. ha. I am very protective of my sleep now. Shooting for at least 7 hours is the goal. I turn the lights lower at an earlier time, that helps. I watch what I eat leading up to bed time as well. I eat very light. I practice good sleep hygiene. https://www.webmd.com/sleep-disorders/circadian-rhythm-disorders-cause#1
Your aunt may benefit from melatonin. It is very helpful for this as well.