I see a bit of symbolism here. Lilies and those are associated with death, more specifically to regain innocence upon said demise and the lily here is stained in blood, suggesting it was once white or, at least, close to that color
To live with the pain of killing the one you loved would be too great for any average person. Eirin, after many long years with her mistress, can't handle that pain. And so, she took her own life, in order to be the she loved. The question remains, what will happen to the ones they left behind?
