Doctor Answers (1) on Psychological problem
Your sister's aversion to fruits is not something alarming, in most likelihood. It's more of one of those personal preferences that people end up making as they grow up.
Having said that, there is a possibility that she might be associating fruits with some bad memory, or event, that might happened during her early years. If that is the case, every time she comes near a fruit, those memories might be triggered, re-inforcing her dislike for fruits.
To carefully understand and evaluate her, you need to take her to a Psychiatric professionla who can have a detailed interview with her, and assess whether this is something to be worried about, or it's a just her food preference.