Late Stage Complications Regardless of Glucose Level Management?

This thread may potentially be depressing for those with depression due to their diabetes depending on the answers as it is a touchy subject.

Hey everyone, my fiancé is a t1d since she was 7 (is 21 now) and when we first started dating I did a lot of research into what I needed to be prepared for later in life. In all of my research, both recently and back then, pretty much every paper or article talks about the complications if the levels are poorly managed, but rarely do I find anything about what may happen even if her a1c is great throughout her life. I'm curious if anyone else knows about what issues she may face even with an excellent a1c. I'd rather be prepared or try to focus on prevention rather than it being too late down the road.