everyone here is right... this is something your sister has to decide to do for herself. she can't rely on you or anyone else to help her with it, and that includes being a quick-reference.
one of the things your sister needs to determine is what's more important to her: losing weight or eating the way she's always eaten. she can't have both, and until she makes a commitment one way or the other (and yes, that includes making a commitment to enjoying food and being happy no matter what her body looks like), she's only going to frustrate herself and you.
an ex of mine didn't see the point in dieting. when i told him about low-carbing, he immediately threw all the typical "lowcarbing is bad for you becase..." reasons at me. he refused to listen when i gave him hard facts. it got to the point where he actually said to me "well, jillian and i discussed it, and we've determined that not only is dieting completely unnecessary, low-carb diets are harmful." i said "well gee, thank you for re-writing the laws of biochemistry for me and adjusting my physical appearance with the snap of your fingers. i'm indebted to you." that was just one of the reasons he's an ex
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how willing are you to give your sister a good dose of tough love? if she's not ready to do this for herself, stop trying to help her. no matter what she asks, respond with "i don't know, look in the book." it doesn't matter if she's asking if the steak you're eating is allowed, tell her you don't know and continue to eat it. you can only give help to someone who's ready and willing to accept it.
meanwhile, let her get all sorts of envious while you get skinny and buy new clothes.