How can I train my dog(Dakota) not to guard food that is sittin in a bag near me?

does your dog respect you? are you the boss? if so try this put on lead , put biscuits on floor in different spots walk her by if she goes for the treat say no and jerk her like in obedience she is not to get the treat.after she figures out they are not hers then give her one say what do you have let me see be quick open mouth and remove biscuit. let her know not to growl or get aggressive, after she gets use to this do it when she is fed. after that is okay introduce the cat she knows your boss and if any aggression is showed let her know it is not allowed. won't take long and she will stop.