My four year old sister is already body conscious! how do I help her?

My sister is only four years old and she has a negative outlook on her body, I can assume she got this discourse from overhearing conversations between my teenage self and older sister and the media. 

we didn't realise she would absorb what she heard us say, but recently she has been saying worrying things like, "I need to exercise" when we told her she doesn't need to exercise as she is only a kid started crying that her "tummy is too big" when we told her its not and she is perfect as she is, she became adamant that her tummy is too big and that she 'hates big tummies' and doesn't want that. she also said other worrying things like "I eat too much" 

How do I stop her from saying and thinking like this?

How do I help her have a healthy outlook on body image and food?