I'm reading "she's gotten VERY aggressive with food and my husband and I" as that she's aggressive when someone else has your attention - does this sound right? Not on the same scale, as Gomez is only 4 lbs, but whenever we introduce a new dog, adopted or fostered, he wigs out and becomes very protective of me. He is an alpha alpha ALPHA male, all 4 lbs. of him. I say not on the same scale, because he cannot inflict as much damage on another human or animal as Bailey Bear would, due to her size, bu I've learned that going around the group, giving love to one dog then moving on to the next, giving each the same belly rub, hug whatever, so that it doesn't appear to him that one is getting more than the other. Gomez sees he's getting as much love and attention as the others, it seems to soothe his bruised ego slightly and it also shows him that the other dogs are "OK".
Food aggression is normal and quite common, even with the most laid-back Pyrs. I discussed this with my rescue coordinator when we brought Morgan in as a foster and she explained that with any new experience, it is one of the things the dogs feel they can control. As she gets used to the other dogs and her new surroundings, it may ease some. Until it does, simply giving her her own space to eat will acknowledge her needs and it may not seem so important to her.
As far as people, especially your small sister - bring her out to meet each and every new person, rather than them coming inside the house. And slow is sooo key. Meet outside, approach Bailey with your sister using a soothing, quiet voice. Make sure she has her hand palm-up and moves slowly. If you sense any tension, stop and separate. Try again until you sense Bailey is comfortable. It sounds cumbersome, but Bailey sounds very Alpha and it may take her longer to adjust to new situations. Plus, she's in an entirely new environment and doesn't understand what the heck is going on. We love them as our own, but they are animals and this cannot be forgotten.
I've had a lot to say (LOL) and I am no expert by any means. But I have 3 small children and have had to take a lot of care with so many animals in a not so large space. Good luck, with time, patience and consistency, she'll be ok.