The Mother-In-Law Conundrum

I can't believe the school holidays are over; *sigh*. We were really getting into the swing of staying in our pj's until mid-morning. Ahem.
I think that was one of our most fun breaks ever. And we didn't even go anywhere. It was so nice to have some down-time and refuel emotionally and physically for the next busy term.
Over the break we had a few visitors, one of them being the mother-in-law. Let me preface this whinge by saying she is a lovely lady and we actually get on rather well. When she visits she always brings our littles pressies which is very exciting for them. Books, stickers, colouring pencils. Nice. And this time a BLOCK of chocolate. Each.
She must have seen the WTF look on my face because she immediately explained that it was organic and preservative-free (at least my banging-on about something has been heard).
Okay, I thought, if I convince the kids to use their choco-booty to make biscuits and cakes I can live with this one (and get in on the action).
But then she rips out this line: "After dinner you can have some". I think this time my head spun 360° and green froth came out of my mouth. I had to put my foot down on this one; "No we won't be having chocolate before bed, we'll do some baking with your special treats tomorrow." The kids looked at me like I had just banned Christmas and had a bit of a sook but the decision was accepted. I think they kind of guessed it would go down that way anyway.
Now here's where it gets rather interesting. After dinner Granny got them ready for bed and read them some books. See I told you she was a nice lady.
The next morning our five-year-old informed me that when Granny went to say goodnight she smuggled them in a few squares of chocolate. After my head fell off and I kicked it around the room for a bit I tried to explain the many levels on which this was a wrong thing to do. Then of course I had to have the awkward convo with "Granny" — she just gave me a bit of an eye-roll and left me feeling like a freakin' prison warden.
Now here's the ugly twist. My mother-in-law is vegetarian. I made her some risotto that night. With chicken stock! What? It was organic and preservative-free. Do you think I'm going to hell in hand basket?
How do you handle your mother-in-law?