My mother visits for one afternoon and undoes approximately eleven months of careful parenting. Last time: three biscuits before lunch (“she looked hungry”), a juice box I have never purchased in my life, and bedtime at nine-fifteen because “she wasn’t tired.” She was tired. She fell asleep mid-sentence during the bedtime story, which my mother took as evidence that the story was boring.

I used to fight it. I would stand in my own kitchen and say things like “Mum, we don’t do biscuits before lunch,” and my mother would look at me with the exact expression she used when I was seven and told her my homework ate itself. Then she would hand my daughter the biscuit anyway, and my daughter would look at me, and I would feel like the villain in my own house.

The flop era peaked at Christmas. I made a whole speech — an actual rehearsed speech — about sugar and routines and consistency. My mother listened politely, nodded, and then gave my daughter chocolate coins “because it’s Christmas.” Which, to be fair, it was. I spent the rest of the day in a mood, and my daughter spent it sticky and happy, and nobody won.

Here’s what I finally figured out, and it took me an embarrassingly long time: I was trying to control the wrong thing. I can’t control what happens at grandma’s, or when grandma comes here with a bag full of contraband biscuits. What I can control is which battles actually matter.

So I picked three. Three rules that survive grandma visits: no hitting (obviously), car seat always, and teeth brushed before bed no matter how late it is. Everything else — the biscuits, the juice box, the nine-fifteen bedtime — I let go. One afternoon of sugar does not undo eleven months. I know this because I have now watched it not undo eleven months, four times.

And then I had the honest conversation, the one I’d been avoiding because it felt disloyal. I told my mum: “I know the biscuits are love. I know you waited years for a grandchild to spoil. I’m not asking you to stop being grandma. I’m asking you to back me up on the big three, because when you don’t, she learns that rules are optional, and then I spend a week rebuilding.”

My mother was quiet for a moment. Then she said, “The teeth one is non-negotiable, I suppose.” It was the closest thing to a treaty we’ve ever signed.

Last visit: two biscuits before lunch (down from three — progress), bedtime at eight-forty, and my mother personally supervised tooth-brushing with the focus of a dental hygienist. My daughter still got spoiled rotten. I still got to be the parent. It turns out grandma and I were never actually on opposite sides. We just needed to agree on which hill was worth dying on, and it wasn’t the biscuit hill.