I am guessing that you might have already addressed some of these first points, but just in case not:
First, I would recommend that you take her to the pediatrician and describe the problem – it is important to rule out any medical issues. Also, you should try to establish some clear boundaries for the entire family on when and where food is allowed. Is it possible that others are eating in front of her outside of meal and snack times? This would probably increase her food seeking. Also, I know that it may be hard to do, but I would also recommend limiting the amount of starchy and sweet snacks on hand – if she gets into the pantry and all she finds is canned goods, raw potatoes, and a loaf of bread, then breaking into the pantry will probably hold less appeal. (if you must have them, keep the crackers and sweets hidden in the top of the cupboard, and don’t let people get into them in front of her).
More importantly, I think you are on the right track with trying to give her substitutes for food – tickling, attention, etc. You might want to continue to expand along those lines. Does she like and properly engage with toys? It may be that she lacks good play skills and that food is one of the only clear (and easy to access) reinforcers for her. I would work on trying to keep her engaged, possibly even explicitly teaching her some new independent and cooperative play skills. Make sure that toys are constantly and freely available, and try to recruit the other kids to play with her, too.
Hopefully teaching her some leisure skills while keeping food boundaries very clear for the entire family will help. Good luck!