Thanks for the additional information. I really appreciate it.
From your girl's viewpoint, the food bowl - empty or full - is her most prized possessions and, even if they show no interest in it, she must ensure that the other beings she shares a house with don't attempt to steal her possessions.
This common type of resource guarding can be traced back to her ancestors' need to protect food and other resources in order to survive. Snapping and growling at other members of the pack was a way for dogs to tell them to back off and leave their food alone. Despite being domesticated, some modern day dogs extend this territorial thinking to favorite toys, bedding and even a certain location in the house, like a sunny spot near the window.
It's reasonable to assume that your girl wants to know if she can chase you away from her bowl and to see if you will yield to her threats. From your description, your Corgi's turf defending is growing in intensity and range. Unchecked, this behavior can become dangerous, with her escalating from growls to snapping, even to biting. As natural as it may seem, do not yell at your dog or physically punish her for guarding her stuff. You risk making the problem worse. She will feel a greater need to protect her treats and bowl since it will appear to her that you are angry enough to fight for it.
This problem did not surface overnight, and it won't go away in one day. Stopping resource guarding takes time. The first step is to establish a new dinnertime protocol You and your family must call the shots at meals. Your goal is to teach her that positive experiences occur when people approach her treats or food bowl and that you reign as the Keeper of Great Chow, worthy of her respect.
Do not let your dog be a free feeder who nibbles all day. Take her bowl away between meals and store it out of sight. During your retraining period, bring out not one but two food bowls - one empty and one containing food. Call the dog to a new feeding place that isn't a high-traffic area in your home. Moving the bowl into different locations in your home will reduce her territorial tendencies.
Place the bowls on a counter or shelf out of her reach. Ask her to sit and stay and then put down the empty bowl (watch the surprised look on her face!). Then drop a piece of food into the empty bowl on the ground. Do not bend over. Wait until she eats that piece before dropping another. If she shows no protectiveness, try putting a few pieces of food in your hand and invite her to take them.
Alternate between dropping food in the bowl and hand-feeding her. When she starts to eat from the bowl, drop more pieces into it. Once in a while, drop in a 'jackpot treat' like a piece of chicken or steak, something much tastier than her regular dog food. It may take several meals before she accepts this new method of dining.
Once she shows no signs of tension, you're ready for the next phase. Partially fill one bowl with her food and place it on the floor. Call her into the room and again have her sit and stay before you give the 'okay' sign to approach the bowl. The goal is to make her work for her food. As she starts to eat, place a second bowl with some premium food about 10 feet away. Call her over to this bowl. As she starts to eat from the second bowl, go back to the first bowl and add special treats to up its food value before you call her over. Continue switching between bowls until she has finished the meal, then take them away and hide them.
Over a few weeks, gradually move the two bowls closer together as you feed her. You need to watch her reactions to determine how quickly you can merge the two bowls. She should be displaying relaxed body posture. This dual bowl tactic is designed to build positive associations and increase her trust that you, or other people, make feeding time fun and exciting, not tense and upsetting. You are using positive reinforcement rather than threats or physical force to show her that food time (as well as treat time) is not a time to fight. She is learning that by giving up resource, she is rewarded with something even better. Eventually, you will be able to present her with a single bowl, though she should always be expected to sit and wait for your signal before eating.
I've followed these steps with several of the pitbulls I do rescue work with, and within a couple of weeks, their guarding behavior either disappeared completely or was drastically reduced. We turned mealtime into a fun game of doggy dining etiquette. They would happily leap into the 'sit' position, watch me put down the bowl, heed my 'wait' cue and my 'watch me' cue before approaching the bowl. Once I gave the 'okay' signal, I was eventually able to pet them as they ate, praising them. It worked for me and my most difficult cases, and it can work for you and your dog.
If you don't feel that you can stop your dog on your own, however, I urge you to seek help from a professional behaviorist. This is a serious behavior problem that can eventually threaten the safety of you, your family, and your visitors.
You should also make sure all toys and such are picked up and not available for her to play with whenever she feels like it. This will likely be temporary, but you have to make sure that you are controlling everything in her little world...including her favorite toys. Enrolling her in basic obedience classes will also help.
I hope this helps!!