If you can take it for what it is, and it doesn't bother you, then keep up the contact the way it is. You have recognized her "faults" and deal with them.
For example, I have a friend I met about a year after I moved here (19 years ago). We became close, went out as couples, my kids babysat her kid. We did holidays together, with other friends, too.
As the years have gone by, what were just quirks in her personality are now outright mental health issues. It is too long to go into. But, other people have asked me if there is "something wrong" with her. I can barely stand being around her. She thinks she is my "best friend," although I hardly talk to her. I have cut down the contact as much as I can, without dropping the friendship entirely. I am trying to get up the courage to talk to her about her issues, but it almost doesn't seem worth it, as she will just get angry at me.
You recognize the bond you have with your friend, so it may be easier to just keep things the way they are.