Mary's Monologue

That's what makes it so hard – for all of us. We can't forget.has hidden deeper within herself and found refuge and release in a dream where present reality is but an appearance to be accepted and dismissed unfeelingly – even with a hard cynicism – or entirely ignored. There is at times an uncanny gay, free youthfulness in her manner, as if in spirit she were released to become again, simply and without self-consciousness, the naïve, happy, chattering schoolgirl of her convent days.
Morphine keeps working as a kind of time machine for Mary, a trope that reaches its peak in the play's conclusion. Her method of forgetting about her present pains isn't some sort of out-of-body experience, like Edmund's sailing epiphanies. Instead, she floats
Mary appears to have an issue with taking responsibility that manifests itself both high and sober. If you look at the second quote in this section you'll see that Mary, when high, also blames fate a lot, instead of criticizing people's actions.

Something I need terribly. I remember when I had it I was never lonely nor afraid. I can't have lost it forever, I would die if I thought that. Because then there would be no hope.

We've already spent a lot of time wondering what Mary might have lost (see her "Character Analysis," for instance), but whatever it is, it's something representative of days gone by. The whole play, Mary's been trying to wipe away the memory of the past thirty-six years, but whatever she's looking for is something that exists only in her mind. This gives Mary an awkward relationship with her own memory – she wants to erase a part of it, but another part is the most valuable thing she has in the world.

TYRONE
What's that she's carrying, Edmund?
EDMUND
Her wedding gown, I suppose.

James can't even recognize that his wife is carrying her wedding dress in her arm. Even if he can't remember the dress itself, how can he not know what a long, white, satin dress would be for? It's as if the idea of their wedding has completely faded from his