Here is what I do, I ask people how many different they can find to make the sum of 10. (5+5, 4+6 etc.)
Than I ask them, which one is right, which one is wrong?
More than once, there are different ways of doing things, with the same good result. So it comes down to what you prefer.
Sorry, but there will be always someone in our lives who knows it all and especially better.
Look at her as you would at a child, still needs to learn a lot.