I take on board what you have all said about giving her more money of her own to budget with, but don't forget she gets pretty regular pocket money in hard cash from her generous grandpa.
Sweets and crisps are not forbidden in our house - some people seem to have the wrong impression - I just don't buy crisps in bulk from the supermarket. Cakes and biscuits are usually home-made.
As for grounding her: she doesn't go out on her own in the evenings, she's still only 12 and I have to let her go to and from school on her own.
I am concerned about her eating habits. She has always had a big, healthy appetite, until recently when she has taken to leaving her meal, and bingeing on junk in secret.
Up to now I have put aside change for her busfares in a jar in the kitchen, and the other day I saw that more had gone than she had needed for the bus this week. On challenging her about it, she made up some ridiculous lie about accidentally taking too much money and giving it to the busdriver who failed to give her any change. So I said right, well I put in enough for the week and I'm not topping it up before next week so you can either use your own money or walk. (School is 2.5 miles/45 mins walk away). It was shortly after that conversation I found her delving into my purse.
Dh and I are seriously thinking of giving her the week's busfares on Monday now, and letting her decide for herself whether to walk or buy sweets with it.
She already has to earn pocket money with chores.