4 year old dog all of a sudden has food aggression issues?

More than likely its either stress induced, or its a territorial issue. She probably feels like she has to protect her food in that new enviroment with new smells and animals. You are going to have to change the ENTIRE way you feed her, and prevent it from happening. You have to make her eat according to 'your terms'. She should see you as the Alpha dog, if not that's problem number 1. Try walking her before you feed her, and make sure YOU are leading the walk, if she gets distracted or tries to go where SHE wants, abruptly stop, or change directions letting the leash do the work until she is 'following' you without any tension in the leash. The purpose of this excercise is to reinforce your positions as Alpha and Lead. Then before you feed her, make her sit and/or lay down and stay until YOU tell her to eat. Hopefully you have been doing something similar since she was a pup. If not you will have to teach her this. Also you should make her eat around other dogs (or cats) but don't cause a 'stressed' or 'tense' situation. Simply put her and the other dog on a leash first. Then after doing the excercise stated above, bring another dog into the same area while she is eating but do so without any noise and try not to get nervous about doing so as this will be 'sensed' by both animals. Simply 'walk' the other animal around the area, if She starts to 'tense' up, or growl even a little, correct her immediately by sharply pulling her leash back to you and away from her food. Grab her by the scruff of the neck and make her lay down. Keep her there until she is COMPLETELY calm, then allow her to go eat again. Repeat this until she can eat without showing any form of aggresion. Also keep an eye on the other dog too, because it may be the culprit as well. These may seem like 'hard' or even 'harsh' techniques, but you can't think like a human, you have to understand how the Alpha dog structure works. There is a huge line between being a firm and strong Alpha leader, and beating your dog and abusing it. Just look at how the Dog Whisperer interacts with his dogs, its all about projecting the right energy, attitude, correct timing and physical contact. Regardless of the cause, a dog should NEVER have food aggression unless he is living in the wild. This can be VERY dangerous for the other animals, your parents, you and especially children. Be patient, but be firm and consistent, and don't think to yourself stuff like, "oh, I don't want to be 'mean' to her" or "she's going to think I'm being mean to her", that is HUMAN thinking, dog's do NOT think like that and they do not hold grudges. They ONLY understand when its being communicated to them by a Strong leader who is firm, and consistent. AFTER she does what it right you can treat her a nice and sweet as you want. But direction, and discipline come first, always. Your dog will be MORE happy if you treat her like a dog, instead of imposing on her 'human like' feelings and reactions.

How about giving her a "safe" place for her to eat. A crate? A special room?

How about hand feeding her?

Have you heard of NILIF?

You should check out some books on resource guarding. As always, you should also look into local help. A good positive trainer or behaviorist.

! Fight! by Jean Donaldson

Mine! also by Jean Donaldon