Dear Blessed Mother...
I have considered what little I know about your situation and this is what came to heart and to mind.
Of course this comes with some disclaimer (at my husbands insistence) as I am not a professional.
What first came to mind is that this has nothing to do with the item of food in question at all.
I saw a kid who possibly is relating to a food as a trigger to feel something "familiar". Some sort of something that is creating a possible sense of security or affiliation or playing out of a role of some kind.
The Other thing I suspect is a power struggle and a need for so sense of control to establish a sense of security and self hood. Perhaps if these things are not in place trying a technique like this...
Giving a choice of two things (within your peramiter you choose the two things) so she can have the self hood. This can begin with even the very simple of things like a choice in shampoo or a blue napkin or a white one. And reinforce it with "you make good choices". If any child is left without option they will struggle for it. Now this could be a deeply ingrained struggle for self hood never met.
For example if a kid who is abused and controlled and forced and made to do or be other than what is true to their own heart... they will look for provocation because it is scary to have life change rules mid stream.
If this sweet kid..."Militant" finds her security in that there are some things that can help her
every kid needs these basic 5 things. They are layer upon layer.
2. a sense of self
This is what makes us able to be adults and not just "grown ups"
When these things are skewed and are attained in a twisted dysfunctional way then that way is what the kid will use to gain it, or the "grown up" will continue to use those methods even into adult hood. Self Esteem gets a bad rap in Churchianity because it is confused with pride or the ego centered on self. That is what happens if all stops and affiliation or a sense of belonging never occurs. this little girl is relating to you in a way that is in effort to gain an innate need. She is not Evil just messed up and broken. She is a good kid with a great heart that is terribly wounded. I do not know the child's age that is also a factor in the developmental milestones and delays. Regression is a common for those who have not developed but just survived.
It is so hard to explain in type I will comment and leave a way for you to contact me. I am not sure that what I am explaining is making the message I intend it to.