I took care of this, but maybe too harshly.
I think the things that helped me were 1) the OFF/DROP IT command, 2) conditioning her to understand then when I approach her eating, more often than not good things happen, and 3) the alpha roll. I can't say I'd recommend the alpha roll, or that I did it correctly. I've always questioned my decision there.
When my pit bull was a puppy, we learned from a dog trainer to play the trading game where we take the food away, over a high-value treat, then give the food back. Never had any problems with that.
Then one day I gave her a dental stick (she loves 'em) and noticed she ran behind the couch to eat it. Immediately I thought, "This is no good". I didn't want her to be protective over her objects, so I went to go grab her to bring her to the middle of the living room to eat it.
I reached behind the couch to get her, and she growled at me. I backed off confused, because it's the first time she'd ever done that. Then I just decided to pick her up anyways. She was probably only 10 pounds at the time. She went psycho on me, bit my hand, and drew blood with those razor-sharp puppy teeth. In only took a second, but she made noises I never from a dog before and got her saliva all over my hand.
I was shocked, and angry. I got a glove, and after she finished the stick I called her to the bathroom - where she couldn't run and hide. I gave her another dental stick and started petting her with my glove on, moving closer to her head. When I got around her head, she started growling. When I got to her mouth, she attacked. Immediately, I alpha-rolled her, pinned her to the floor and gave two very loud NO BAD DOG's.
She submitted. I let her up and gave her treat back. Her demeanor changed and I continued to pet her as I gave her some more treats.
For the next few days, I made it a point to feed her dental sticks from my hand only. She could chew them while I was holding them.
It's six years later, and she's never growled at me since. But I've always wondered if I was too harsh on her that day, and if I could have done it in a less physical way.
I don't play the trading game anymore. I never take her actual food or treats away. I do occassionally pet her all over, including around the mouth, when she's eating food and treats. I also give her treats from my hand while she's eating. Everytime I pet her while she's eating, her ears go back and tail wags. I take that as a good sign.
If I need something she has, I say OFF and she drops the object, backs away and sits. If I just wanted to clean the item off, then I clean it and give it back to her, often with more treats. Occassionally, I just take it because it was dangerous/dirty (i.e. cat shit). If she's about to swallow, then she won't drop it, so I just stick my hand in her throat to fish it out.
I like that I can get close to her around valuable objects without any aggressive behavior - so I practice that. However, if I really need to take something, I ask her to drop it first so there's no confusion. Even when I fish crap out of her throat, I give her the option to drop it first, so she's knows it's coming.
If I were you, I'd probably train the OFF/DROP IT action, I'd feed her low value kibble and give her high-value treats by hand while she's eating, and I'd learn more about what can be done to establish your dominant position and pack structure. Doesn't have to be in that order. In fact, I'd start them all immediately.
But take my advice in the proper context. I'm just a first time dog owner of six years, still on my first dog. I just ordered Leerburg's video,
Establishing Pack Structure with the Family Pet. Without having seen it, I'd say Ed's advice trumps mine, and that DVD is probably the one you want.