It's a lesson taught by some religious (e.g. Sunday School) teachers. It goes something like asking a group of kids "well you don't want to eat a cookie that has just a little bit of poop, would you?" Relating it to some "worldly" practice, from my hazy ADHD memory I seem to remember it being swearing in my lessons, but there's many variations I heard from other people.

So the idea is "just 1" worldly thing is 1 too many and you must stay 100% pure for the big G.

In this case, she's saying the metaphorical poop in our society "cookie" is trans people existing.

It's utter christofascist puritanical horseshit.

Starting at the second sentence of the article:

Johnson was banned in 2023 over comments where she compared the issue of transgender students in Alberta's schools to baking cookies with feces inside.

“We can be top three per cent but that little bit of poop is what wrecks it,” Johnson said in audio from a 2022 talk at the Western Unity Group in Stettler.

“This is more than a teaspoon of poop in the cookie batch, right?"