It takes a long time. I lost a friend (human) suddenly. Even after being at her funeral, and being part of scattering her ashes.. I would still find myself thinking of her as being at work (she took over my job when I moved back home to get married).
I expected to see Riven for a long time too, and assume I will catch myself expecting Aria's nose on my back.
All this shows is how deeply you felt her presence in your life. Even though it makes you sad, memory is a blessing.