Anne, I am so sorry to hear about your Granny. I will light a candle for her and your famlily (and you of course).
I recently lost my Granny at the age of 85, and I miss her so. I know the feeling of guilt for not seeing her more often, and the "just to talk to her once more" feeling. As many have said, we cant lose our selves in thoughts like that. Your Granny will understand. Now she can watch over and see both your sons grow up.
Your Granny was a very brave woman, and at the age of 90, probably was ready to leave after a full life, but it still hurts to say goodbye. I know you will pass the good memory of your Granny on to your sons, so they will feel as if they knew her.
God bless her and you all and help you in your difficult time.