For an older dog:
1. Make her “sit” before you give her the food bowl.
2. Only feed your dog after you have had your dinner. Make sure she knows you are in control of the food and when it is passed out.
3. Stop leaving food down all of the time. This is based on the “pack” theory, similar the first two tips. If your dog recognizes you as the one who is in control of her meals, she is more likely to respect you as the leader and will no longer be aggressive.
4. Feed twice a day so your dog does not get too hungry between meals. Some food aggression is caused by your dog not knowing when her next meal will come along.
5. Put her feed down in a quiet, secure location (like a back porch, not a busy area like the kitchen) so she does not feel threatened. You leave your dog alone and don´t even pick up the bowl until she has gone into another room. This may be all that is needed for some dogs.
6. Use counterconditioning techniques to let her get used to your presence. Step up just short of the point where she feels threatened; throw her a special treat (like a piece of baked chicken breast) and then walk away. Do this every day until she associates your approach to her food bowl with the handout of a special treat. Over time she will feel less aggressive and will not mind you coming very close to her bowl. This is a slow method, and needs to be reinforced occasionally, but may help if the other methods listed above are not enough.
If counterconditioning is successful, I have also heard some trainers suggest you take the dog´s bowl away and add treats to it while she is still eating. I think taking the dog´s food bowl away, for any reason, is not a good idea. This is supposed to be another method of making the dog more confident in your control.
7. An alternative food bowl may be helpful. I have put a capsule from EBay for the Aikiou, a bowl that makes the dog think about her food, not about what is going on around her. There are a lot of other alternatives that might be more successful so do not buy a bowl and expect it to solve your problems.
I am assuming she is aggressive to you and not to another dog. If it is to another dog, sometimes it helps just to feed them separately, and to take the dogs food away after 15 or 20 minutes.
Good luck with her. If you have any questions you can leave me a note on my hub about food aggression.