Here is a helpful video on setting a quilt on point. It is not
as difficult as I thought it would be, and I made one 110” x 112”!
https://youtu.be/0AfBeYeCzRE
Here are nice directions written out to do it with sashing. When you go to the site, scroll down a bit to find it. She starts one without sashing, then does another with sashing. Just take it one step at a time, and make a small quilt to learn it, then you can make grandma a pretty placemat with it. It is not as hard as you think.
https://quiltnotes.com/learning-center/on-point-quilts/