Jamie's dog is food aggressive, what can be done about that?

Jamie writes: We've only had Koda for 6 months but she's about 4 years old, we think.  She is a great dog in every way except she doesn't do well with other dogs and it seems like she has personal space issues with them, and she guards her food and water from the cat.   

She  went after a dog that came up behind her a couple of different times, and growled at the cat (who she normally is fine with) when he came into the room while she had a rawhide bone.  

She is never otherwise aggressive, seems fine with children and all people, even large groups.  I would love to help her get over these behaviors - she's really a sweetheart but we really want her to be ok in these situations.