I know many home educators get hold of the book called "Free Range Education" Edited by Terri Dowty, where 20 different families talk about home education and how it has worked for them. There are all types of home educators represented there-the very informal/autonomous home educators and the more structured ones too.
My mother tells me it helped her to understand.
The problem is, that most people have this stereotypical image in mind when they think about home ed-I know because I had it too before I deregistered our children in desperation!
They believe that the children sit all day long at a desk/kitchen table, being taught lessons by mom and cut off from society.
Most would be absolutely astonished to find what a great supportive community of home educators there are out there.
Someone somewhere mentioned that finding the home ed community, is like Alice going through the 'Looking Glass' and finding a whole new world through there!
I took my mom along to a home ed meeting a couple of times and she began to see for herself the mass of children of all ages playing with no gender/age separation situation. She got to talk to other home educating parents too.
She also got to meet more and more HE youngsters at our house and found them to be confident, well educated and lovely to be with.
Some families choose to say that they will HE up to the age of say 7 and then review-meaning Granny gets a time to see their education develop and is more confident when you say, "we have reviewed it and we are going to continue". This was never an option for us as we rescued our children later from school and they were adamant that they were never going back!
But to be honest, it is only time and experience that will change this-when she will begin to see the results for herself and her grandchildren become self confident, well educated people.
Until then, you may just have to say that you are sorry that she feels that way-and then move on.