DD is 15 and since toddlerhood has had quite an egocentric streak in her. Now she's older it's worse than ever.
Yesterday she found some sweets in DD2's schoolbag, bought to give to a friend for her birthday, and she took them and ate the lot. She did the same with some sweets given to 5yo DS not long ago. This sort of thing has happened countless times. Anything not under lock and key is fair game to her - food (biscuits, crisps, anything 'nice', things bought to share), my make up and clothes, anything in the house that she wants is liable to be pilfered, then lied about.
No punishment or consequences have so far made any difference. Occasionally she will show some remorse, say she can't help herself and promise to reign it in, but it only lasts until the next time she wants something that isn't hers to take. I don't know how to deal with it any more, or help her, if she needs help. I am sick of it. We all are.