text: Any number of reasons, she may be on a diet or she may feel uncomfortable eating large portions in public, as she worries that people will look at her wondering why she doesn't eat less. You know how judgemental people can be. She may be ashamed of her eating habits and only does it behind closed doors or in secret, not where people can see. Have some compassion, it must be hard enough for her, without ignorant strangers gawking at her. Take care.