Estranged Grandmother

My dad has recently been in contact with his estranged mother who only lives less than 10 miles away. We have tried to contact her over the years and no one really knows what her deal is other than she had a strange life. She left when my dad was a teen and remarried and pretty much has always made excuses that she was too busy. I have contacted her many times over the years and tried to witness to her, tried to get her to join the family and let her know that no matter happened we forgive her and we can start over again and that there is no reason to abandoned yourself. She agreed 7 years ago to visit after Christmas, it was pretty quiet cuz she doesnt communicate. So for awhile she sent cards at holidays and that was it. I would invite her to stuff but she was busy.
My dad called her a few weeks ago on her B-day to see if she wanted to go to breakfast but she said she doesnt eat breakfast, so he said well how about lunch, and she said well I dont really eat lunch just a glass of milk, so he said well how about I just come over and she said yeah- Id like to see you. So he visited for an hour cuz it was pretty much not much to talk about.
Well he found out she has inoperable colon cancer. All week Ive debated wether to go visit her, Ive been thinking about it since Christmas but couldnt decide wether to visit , call, write. So I think I will go visit. I saddens my that my dad had to have that kind of relationship especially since he probably hasnt probably told us how he really feels about it. I keep thinking what if something happens we will never know what her deal was- but we may still never know. I would like to ask her if she knows what is after this life but Im afraid Im going to get mad at her. I tend to get mad when I know im right and someone doesnt listen- I know I cant make them and its their choice but I feel like what if know one ever tried to get thru to her?