First, you gotta relax! Take a breath and stop for a moment.
Ok, so she's a Chow mix and you gotta take that into consideration, but she's not just a breed. She's an individual.
You used the term "pack leader" so maybe you've watched Cesar Milan? (Don't judge. I'm not endorsing him, I'm just trying to relate!) I may not agree with everything Cesar does, but I think he has some good points. One thing he encourages is to picture the positive outcome you're seeking. You've got a *whole* lotta negative going on with you're fears and you're almost setting yourself up for failure.
Dogs are not wolves, but they're close. They are pack animals and from the research I've seen the dog of today is very, very attuned to human behaviors. They take their cues from their leaders. In this case it seems like you're going to be tense and nervous, which will translate to your guard dog breed to be alert for danger.
I don't know what to do about the bratty chihuahua. Sorry.
As for feeding, I'm glad you are learning more about canine nutrition. I will say, it's generally us that make our dogs "picky." Think of it, dogs are actually one of the most successful animals on the planet. They left their cousins, the wolf, behind and ingrained themselves into human culture. They are masters at interpreting human behavior and they are master manipulators! Be assured, NO dog will voluntarily starve to death if there is food available. I don't know enough about your situation to speak to it but usually out goes like this... Food is offered that is new, or different. Maybe it's not exactly what the dog would like so they turn up their nose. The ever dotting human sees this and immediately fears the dog will starve so they offer new food, or "higher value" toppings like gravies, or table scraps. This continues until the dog is eating steak while the human has cold cereal. OK, a bit exaggerated but that's the general idea. Offer the kibble, put it down for only a half hour or less then pick it up and put it away. Do this once or twice a day. No treats. No scraps. Nothing but the kibble and that is only offered for a limited time. Eventually a hungry dog will eat what's offered. You can reintroduce treats but I wouldn't give any around meal times.
Hope this helps a little.
ETA: I've got more ideas, but it's hard to swype this all out on my Android phone. Plus it's almost 5am and I need some sleep!
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