See.... my perspective is the 8 year old corrected the girlie - scared her and scared you. But note that there was no harm done to the girlie while he made his point. This is what the older dog should do - perhaps not in so scary a way, but to a certain extent it is a very important life lesson for her. She's got to learn to respect her elders. For a dog pack to get along very well, the dogs need to know where they stand on the totem pole.
I very much doubt she will try stealing from him ever again.
Other thing is be fair. When you buy a bully stick for one dog - buy for the other. Give to each and send them off to their own spots to chew on their own.
^ This is my two opening up Christmas gifts. That was a bag containing chews. I have very sweet and very mellow tempered dogs - but even they have a totem pole. The dog tearing into the gift and getting first dibs out of the package - he's top dog. These are dogs who can eat out of the same bowls with leftovers and baby Glee is typically the one grabbing the bowls altogether and strutting off to eat in privacy. But when it comes to bones or things that are very high value to the dogs, he holds back and lets his brother get first dibs. And they have a very peaceful existence together.
That's probably where you will get to with your dogs. Give them bully sticks - but be aware that your older dog is top dog. He gets his bone first and gets sent off to his corner and then you give to the girlie. You might need to referee a little to make sure the boy doesn't go back to claim the second bully stick for himself as well, but generally speaking once the dogs have gotten each other sorted out, there should be an understanding. And then it is up to you to keep it that way.