Sad to read your story and the ones in the comments. I was first in my family, by decades, to marry out of my race. With the exception of one uncle, any racist thoughts were kept to themselves. Now I am not alone in it and there are more challenges for some in the family I suspect, but love for each other seems to have overcome that stuff. Sad when it doesn’t. Some say that friends are God’s apology for family.
Your grandmother is from a different time where her attitude was the norm for her subset of society. Who knows how we will be judged by our grandchildren. Hold on to a bit of love. When you forgive someone it’s not for them, it’s for you. Someday she may see the light.