48.5 % of the film
It is just the first of many lost glances that will define Fiona throughout the film. Julie does the whole lost & Alzheimer thing with great talent, and it all looks so efortless (which is probably why she lost the Oscar).
Fiona loves her husband, but it's more to her that meets the eye. As she's slowly diving into forgetfulness, some memories about her husband cheating on her years ago just won't go away. In the first part of the film, Julie decides to alternate Fiona's long glances with moments of unexpected sincerity. With just one look, she can blame him for all his mistakes from the past. All the malice is justified in the story by the development of the disease.
If there's something good about Sarah Polley's direction is that she loves close-ups. For us, that's a blessing because it allows Julie to glow & quietly demonstrate us that she knows exactly what she's doing with the character. She is Fiona, as she capably maneuvers each of her face expressions.
Fiona seems calm and resigned with her disease, but this is until, at the nursing home, she has to say goodbye to her husband, as he won't be allowed to see her for a month. We've felt her vulnerability before, but now we see Fiona's first tears, as she tries to stay strong for her sake and especially her husband's.
Now, I don't like to spoil movies (maybe someone who hasn't seen it will read this), so I won't say much about the second half of Julie's performance.
But as the Alzheimer becomes more and more serious, Fiona goes into deeper emotions. From a schoolgirl smile, to a heartbreaking expression on her face, and to a river of tears.
Obviously, it's all done with perfect grace and it all seems natural, there's nothing overacted, nothing fake about Julie's performance; from the grey of her hair to the honesty of her reactions, the way she moves and talks.