Count me in with the ones who do not believe in punishing a growl. All you're going to do is create a dog who is fearful of expressing itself. When my dog growls (which is very rare, because I usually spot his behavior prior to growling and act accordingly), you know what I do? I back off! A growl is a symptom, not the underlying problem. You need to take a step back, think about what caused the growl, and then take a different approach. You need to work on changing her underlying emotions around food.

By punishing her, you are, at the moment, actively creating a negative association with people being near her while she is eating. This will create a dog that is defensive and timid while eating. I've seen it in plenty of dogs, including in my OWN dog, after I used force-based training methods to fix his mild food aggression (and, no, I didn't do it "wrong", I actually have good natural timing, which has come very handy in clicker training)

Here is an good excerpt from Sophia Yin's article on how to deal with resource guarding. This is method 1 -
"At every meal, while Fido's eating his plain dog food, stand a safe distance away and toss a steady stream (10-30) of bite-sized treats that he loves. Then, when he's finished and has nothing left to guard, move closer and toss more treats to him or into his bowl. Note that you'll have to cut back on his regular food so that he gets his normal daily caloric alottment of food. After a few meals using this method, move a bit closer each day, always staying outside Fido's defensive range. If Fido tenses up or even growls, then you've moved too close, too quickly, so watch his body language closely. The key is that he stays relaxed at all times around the bowl and learns to expect even better treats from you. If this method takes you any more than a week, or Fido looks tense, or you're in any doubt about your ability to safely read Fido's mood, then you should go to method 2."

I also suggest "trading" the food bowl for a high value treat, and feeding by hand.

I also need to add this. Sowa, it seems as though you are very concerned with your dog's behavior. That's very good! But what's worrying me is that you appear to also be concerned about constantly making sure you are the "boss."

Please, do yourself a favor and don't think that way. I did the same thing for many years of my dog's life. I was a rabid Dog Whisperer fan and was constantly correcting my dog. Our lives were not happy because I was always so concerned about whether or not I was the "dominant" one. I read a great book by ethologist and dog behavior specialist Dr. Patricia McConell called The Other End of The Leash and it really changed my mindset. I stopped worrying and just starting enjoying him. He's much happier and so am I. This does NOT mean he does not have boundaries and does whatever he pleases. He doesn't, but I rarely have to redirect him anymore because I'm always making it clear what I want him to do, not what I don't want him to do.

Instead of looking for reasons to say NO, look for reasons to say YES! That's the fundamental idea that has totally changed the way I relate to ALL the animals I work with, whether it be dogs, cats, horses or birds.

I'm only saying this because I wish somebody would've told me this earlier. I wish somebody would have recommended books like The Other End of The Leash and The Culture Clash. I don't know if I would've listened, but I hope I would have.

Sowa, I really hope you can enjoy your dog as a puppy as much as possible. It's such a precious time.