I am sorry for your loss. About a year and a half ago I lost my husband unexpectedly. Twenty years prior I had lost my father. Losing my father taught me a lot about grief and loss that I was then able to apply to losing my husband. The main thing I learned is do not stuff your feelings. Make sure you allow yourself to intensely feel the loss. Cry if you need to. Find someone to talk about it with (friend, family member, therapist). Writing letters to your grandmother might help in days when you really miss her. I wrote a few to my husband.

Just don't deny your grief. You have to feel it eventually. With my father I denied it for ten years and suffered greatly because of it. Once I was able to process the grief I did much better.