Honestly, I think I would have to work with your dog to have a sense of what's going on with it. It almost sounds in these messages as if your dog is escalating - would that be correct?
If this was my dog, or a dog I was training, these are the possibilities that would run through my mind (and please, please, please don't take any of them offensively - it's a mental checklist - it comes out a lot politer when I'm talking to clients)
1. Bad breeding. I would want to know who the breeder was, what the lines are like, what socialization was provided, how soon the pup was separated from the parents, whether the dog was a singleton, whether these behaviours have always been present or whether the behaviours have escalated since you've owned her. If it's been since you've owned her, I would want to know when you took ownership, and when she started to escalate.
2. Medical problem: The only dog I ever coached who escalated instead of de-escalated had a tumour in his brain. I would bring your dog to the vet, and ask him/her to run the complete gamut of tests. I've seen great dogs turn mean because of a pulled shoulder, back injury, sore paw, and bad tooth. I'm sure the vets can add to this, but I would definitely be doing a full check up including all relevant blood tests (this is actually the first thing I would do if it was one of my dogs).
3. Training. If it's not the breeding/socialization, and it's not a medical issue, now I go to training. If the dog is escalating, there's probably a real miscommunication going on between you and your dog. Your dog may be anxious, frustrated, or confused, and using these aggressive displays to account for the problem. I would say this is the problem with at least 90% of the owners who come to me saying their dog is aggressive - it's not a dog issue, it's a communication issue between the owner and the dog. You need a
good trainer. The problem is, of course, a lot of trainers say they are good (and probably think they're good), but the reality is they have no clue what they're doing. By the way, "behaviourists" don't always know what they're talking about either. I'd ask them what methods they plan on using - counter condition and positive reinforcement is good, flooding and dominance is bad (and potentially disastrous, from what you've written). If they have no clue what you're talking about when you mention those terms, walk away.
4. Environment. If all else fails, the environment needs to change. Bailey can't be put into a position where she will react this way. The more she gets used to reacting, the more deeply engrained the behaviour will become. That may mean that you have to take the stairs, or get up at three in the morning to practice appropriate elevator entrances and exits. It may mean that you have to beg your friends to act as "strangers", so you can practice appropriate behaviour skills. You need to set her up for success - avoid what's setting her off (for now) and build her confidence in other areas, then gradually reintroduce the problem area.
I remember you saying that the trainers and behaviourists in your area are ridiculously expensive. I'm so sorry about that - most trainers here charge about $50 - $60 an hour for a private lesson (and those are top level trainers!). Really research your trainer - having a bad trainer will be a financial hit and have a negative impact on an already difficult solution. If the cost is prohibitive, consider a group class - I've had tons of reactive dogs in my group classes, and it actually works out well because it's a fantastic opportunity to practice behaviours. If you can afford a group class with an excellent instructor, instead of a private lesson with a mediocre instructor, that's the route I would take.
I know you're really worried about Bailey, and I wish you the best of luck. This whole situation must be so frustrating for you. I think you're doing a great job of seeking advice and exploring options. I hope this gave you at least a few more ideas, and again, I apologize if it came off as abrupt - it's not meant to be - I'm just exhausted and about to hit the sack once this is posted
