How much research have you done into modern parenting techniques?
You live 200 miles away and so you're not involved in the day to day. You don't have a strong relationship with your dil which means she doesn't trust your parenting style. Your techniques and style is alien to her and this is her first child. Every new parent is anxious and so they will defend their way of doing things quite forcefully, as the world is so judgmental of mothers!
I was a new parent 20 years ago and I'm also a new parent now at age 45, so I'm seeing how the new generation parent and I actually hate it. I didn't much like the parenting styles of the 00s either and being a Gen X kid, I'm picking and choosing the best bits of old and new.
But that's another story.
My advice to you is to try to understand that you were a new parent once, and it is terrifying. You worry your child is going to die, you worry about doing things correctly. You overthink, you worry about food and can't sleep for worry.
As you get older you wonder why you were so rigid. But you have to understand that is how new parents are.
You must be the student who follows the lead of the new parents. And your son stood by his wife and you should be proud of him for doing so.
Ask them about their parenting styles. What their concerns are and listen with enthusiasm. Say, "ah that makes sense!" Respect their choices, say you're proud of them. Ask what you can do to make amends for the future.
Be an open book and say you're there to help and lighten their load and thank them for being honest with you.
You can do this!