Agreed. She'll probably not know why she's doing it, so there's no point asking her about it and reprimanding her. Probably it's just a temporary phase which will pass off as she grows older. However, for now, you could insist on her showing you every time she's eaten an apple (for instance) and then throwing the core in front of you into the dustbin. You could make it a rule that every time she eats an apple she has to come to you once she's finished. 3-4 times she's done it, she should be fine.
Have you always had her, or is she a foster/adopted child? Hiding food, or hiding garbage, or hiding dirty laundry are things that kids in orphanages or who have had very rocky early childhoods often do.
Piling apple cores in a specific hidden place isn't really laziness - it's a desire to hide. And she may not know why she's doing it.
If you've always had her from birth, and she's had a comfortable, loving, positive home, I don't know what might be causing this.
How is she doing in school?