Our 18mth old maltese cross has always had resource guarding issues. It is not while she is eating her food from her bowl, but when she has a bone or pig's ear etc. She becomes very aggressive and has bitten our child. Once it has happened, she is very remorseful and we ignore her. She has become a great dog in every other way except with food that she values. She used to be like this when woken from her sleep but we have trained that out of her.
I don't know what to do next. We have just avoided giving her food that she doesn't eat immediately.