[Ms_P]

She probably thought you were going to take the treat. Just because you don't "tease" her with food doesn't mean she will not be a food biter. Have you ever put your hand near her food bowl when she was eating?
You should have scolder her. What do you do if she gets a hold of something that you know she shouldn't have, like a chicken bone or something that could be poisoness to her?
You should work with her on the "Leave it" command. So she will drop what ever she has in her mouth when you say "leave it".

 

[Ms_P]

How old is she?

 

[Ms_P]

The crazy age.
That is when they start teething.
The breeder I got Koke from was telling me at this age they can do some things completly out of character for them. Like a toddler.
You just have to get strict with them, and don't let them get away with unacceptable behavior.
You could try letting your son feed her and putting her on the floor before he pets her.
She is being posesive of you. And to her your son is a litter mate.