How to explain to kid why subtraction is not commutative

The idea that it isn't commutative seems, to me at any rate, to be more intuitive than the idea that it is. Try this: If you laid out 5 coins on the table, you can take away 2, but if you laid out 2 coins on the table, you can't take away 5!

EDIT: Also, if she understands negative numbers, you can explain it using that concept as well (e.g. I can gave you 7 dollars, and you can give me 5. what would it mean if I gave you 5 and you gave me 7?)

Sounds to me like she's smart enough to understand that addition is commutative. So, for example, $$7 - 4 = 7 + (-4).$$ Then $$7 + (-4) = (-4) + 7.$$ But $$4 - 7 = 4 + (-7)$$ and $$4 + (-7) \neq7 + (-4).$$

To make things simple, let's consider a way to make sense of $$1-0 = 1 \ne -1 = 0-1$$ in real life, say the temperature.

• $1-0 = 1$: yesterday's temperature way $1\mathrm{°C}$, and there's a $0\mathrm{°C}$ drop in temperature today, so the temperature now is $1\mathrm{°C}-0\mathrm{°C} = 1\mathrm{°C}$.
• $0-1 = -1$: yesterday's temperature way $0\mathrm{°C}$, and there's a $1\mathrm{°C}$ drop in temperature today, so the temperature now is $0\mathrm{°C}-1\mathrm{°C} = -1\mathrm{°C}$.

Both cases give different temperatures.