to some dogs yelling is just barking with them.. which is why it is not usually the best way to make them stop.
diverting her attention might be best.
But lets start afresh. you say she is a sheltie/corgi? you think? do you have a picture of her so i could better tell what mix?
also if she has even a slight drop of sheltie blood in her then you're stuck with this personality. she's not only a herding dog, but she is a protective dog, she is naturally suspicious of strangers so dont put her in the arms of strange people again. that is like expecting a bulldog to not react if he is threatened by another dog.
When a sheltie goes after someone like yours did she is trying to chase away the new strange threat. my sheltie would do this and had a particular dislike for children above all else. she was also a barker and a howler. she was very vocal in all situations. the only way i managed to keep it under slight control was that i got her as a puppy and treated her the same way a wolf treats a puppy or other pack members.
shepherds of any kind have a good firm hold on their wolfish instincts and they thrive with that sort of teaching method. Maggie, my sheltie, could be control with eye contact and tone of voice, not to mention if i pointed at her she would stop dead in her tracks and turn the other way in a hurry. didnt matter what she was doing, just walking too close to a place i didnt think she needed to be, or eating. if she was eating something and i did the "look" and pointed or lowered my voice - food came out of her mouth and she would back up like "Whoa, sorry boss" she would drop prime rib if i did that.
again she was trained this way as a puppy.
for your dog i would suggest diverting her attention when she starts to do something stupid. you may have seen the dog whisperer do it before, but i trained all of my dogs in his methods BEFORE he was famous. it works.
When she begins barking at someone step in front of her and give her a nudge with your knee and try to make her back up. essentially you're herding her... and you want to block her view totally. generally the dog will stop barking and look up at you like "WTF? i'm sorry i'm sorry! lay off, what the crap!" then try a sit or down command.
i also agree with Mikado.... take her out into a public place with lots of people but dont let them touch or approach her.
she may never accept strangers petting her, but that doesnt mean she is crazy or a bad dog. it just means she's a shepherd and they arent supposed to allow that sort of thing from a stranger. again, think wolf pack. when two strange wolf packs meet they dont automatically start frolicking and accepting one another. they are standoffish, then sniffy, then they do their dominance display. same thing with dogs and especially herding dogs. unless you're about to marry this person, adopt them, or some how live with them for a long period of time she doesnt have to accept them touching her. they arent family and are therefore unworthy of her love and affection.