Most Helpful Guy
i'd say something along the lines of... I think everyone looks back on life and things about how things would have played out differently if they had done this or that a certain way. but such is life, we made decisions at that time that we felt were right for ourselves. but as much as we can romanticize how something would have gone in hindsight we made the decisions we did adn there really is nothing we can do about it. make the best of your situation now and use your past to help you make your decisions going forward.
essentially what I think she is doing is going through a rough patch with her hubby and now looking back is seeing these silver linings of her past. she remembers a happier time and so it seems like an ideal thing but in reality it probably wasn't. I imagine you'll find the right thing to say but mostly I'd just remind her that things happen for a reason