Lots of great recommendations from Jadotha, SmokeyCat, Joshuagough and others!
I'll just add in a thought to may help you get in Maci's mind...
My guess is that she was not born this way - but something in her early litter experience made her believe she had to fight to hold onto her food... there may have been other dogs besides the mom and litter mates in with her that she had to compete with - especially once weaned, older dogs would have been interested in the smelly mush they normally wean them to.
I would try and "mother" her (or "father", but "mothers" normally have softer energy) - hand feed her, and if she growls, just slowly move the food away so she can't reach it - wait for her to be calm and maybe even look at you instead of the food, and then calmly say "good" and give her another handful. At this point, you might want to feed her until she can't eat another bite, too... so she knows she won't go hungry. If the other dogs come to see what you're doing, make sure YOU are the one that tells them to stay away - before Maci needs to growl at them herself, so she learns to trust that you'll protect her, too.
Reward EVERY little good thing she does - become a source of happy, calm, loving thoughts. Fill her days will positive good things. As others have said - avoid anything that might end up with a bad reaction (i.e. picking her up or sneaking up on her when she's eating).
I would do a lot of "come" drills. Put the other dogs away, then have you and your wife sit on the floor, each with a bucket of kibble or treats (you can make this "dinner" if you give her enough kibbles this way)... use baby talk to get her to come to you - say "good Come" or "Maci!!!" in a happy happy voice, and give her some treats - then have your wife start calling her the same way... 'pass' her back and forth between the two of you, so coming to each of you is a GREAT thing - full of love, praise and food.
Then - send her to her crate with a nice toy or chew treat, and lock her in for a nap and some calm alone time. That will give her time to absorb all the goodness and reflect on how wonderful life is now that she doesn't have to fight for survival.
And, if you do need to get a bone or something away from her, and she does the growl/charge... don't back down, don't get angry, don't yell, don't say her name. Just stand your ground, move in very slowly and wait for her to back away from you, there will probably be a moment when her light switch goes off and she surrenders - then you can calmly pick up the item... count to 3, then have her look at you and/or come to you and give her calm praise for that.
And, I'm not a trainer either... so take what works for you and modify as needed.
Glad that you have had some professionals come over that seem to be helping!
And, she is a cutie. Looking forward to some happy pictures and videos of her in the near future.