I believe that our bodies "talk" to us, and the fact that your neice doesn't want chicken means something. Chickens are given lots of hormones (and who knows what else). Maybe she is reacting to those hormones and chemicals?? Not only in chicken, but in so many other things that we eat. Maybe it would help for if your sister tried putting her on a strict diet of organic fruits, veggies, and whatever other organics are available in your area.
I'm just curious-- why won't she do any of the cleanses?