Hi Jodie, i'm sorry to hear that your niece suffers from Eczema, i have also suffered from it and it is not nice at all.
Has your sister tried emu oil? I found this to be fantastic, you can get it in creams, oils, shampoo etc and it really stops the itching and flair ups.You can get it fairly cheap on ebay, this is where i get mine, if you like, i can PM you a link to an ebay store who only sell the emu oil products

I hope your sister finds something that helps soon