Get your food processor out and shred zucchini, mushrooms, yellow squash...all of them cook down to almost nothing in things like spag bol, you can add them to meatballs and they will never know they are there.
Do you make pasta? Pumpkin and spinach ravioli is a winner here - again, she has no idea what is in it. You can put anything in them, just finely chop and cook them down in a pan until quite dry.

How about soups? they are great as again, the kids really don't know what is in them.