Summary: The death of the mother is the terrible loss. Below presented the sample of the letter will help you to find the words for the expression of your sympathy and deep condolences to the person who had such a terrible loss.
23 Road Brewers
I was shocked by the news I hear yesterday about the loss of your mother. I am deeply sorry for your loss.
Your family was always close to me and your mother treated me like her own daughter. She always was wondering how I am doing even after I left New York. I will never forget her attitude, warm welcome each time I was coming to your house during my vacations in New York. She was really caring, attentive and lovely person. Even last year during my visit she looked so strong and happy although she was sick that time.
I share your grief and sorrow. I am arranging the ticket now in order to be able to be present during the funeral.
PLease, take care of yourself. If I can be helpful with something, let me know.
With deep sympathy,