My dog acts weird when she has food she really likes?

I have a 2 year old Cairn Terrier. She is an excellent dog, very sociable with children and other dogs and is well trained. The only problem I am having with her is that when we give her a bone or a raw hide stick she gets possessive. She growls when we go near her with it and won't give it up. She is fine with her every day food and we can take it whenever we want. She even waits by her bowl until we tell her it's ok for her to eat but for some reason she gets weird with anything she really loves. Is there something we are doing wrong and can it be fixed. I now have a 2 month old Cairn Terrier as well and I don't want her to pick up the same habit. Plus if I ever have Children I don't want to have to worry about giving the dog a bone when they are around.