
Well, yeah. Gravity affects the passage of time, and gravity is not uniform throughout the universe. Some areas have much higher gravity, enough to cause significant differences in the “age” of certain patches of spacetime, especially over the age of the universe. The real question is, does the age of a patch of spacetime change anything else about it?
You even called it out as an uncomfortable question. You’re as far from wrong here as one can be. I hope your sister comes around and can have an equally uncomfortable conversation with her husband.