Welcome, I'm glad you posted and I have a few thoughts for you.
I started to read this paragraph and thought, meh--who cares, it sounds like they get along good together. But reading on, it just kind of sounds like they were raised by wolves maybe. They sound downright uncivilized.
But then...there are more problems with your scenario I'm sorry to say.
This is somewhat my personal opinion, but it's a lot of people's opinion at least where I am (supported by employer, even!): I don't think it's one bit appropriate for the employer to have registration/billing clerks initiating or dealing with their payment processes at some of the times you are talking about; not at all. Yes, the following kind of thing is a problem:
...and the problem is that your employer should not be asking you to be in that room doing that when the patient's treatment is just beginning to be initiated. I am surprised if your place has cash/cards changing hands when IVs are just getting started or the patients are in the timeframe of receiving their initial treatments. The patient's treatment takes priority over everything else generally speaking.
You are correct. Many employers have decided the best way for these two groups to work together is to develop a system where registration staff can be alerted to appropriate times to be in the room. At some big systems, registration staff is to follow this process and if they still happen to find themselves in a patient room when elements of treatment need to take place, they are to immediately excuse themselves and return later. I'm often the one telling reg. staff "no--go ahead and finish what you are doing, it looks like you're almost done." They, for their part will either say, "yep, I'll just be a few more seconds" or "eh, we're just getting started here, I'm happy to come back later."
We DO have to work together, and we absolutely should be being polite to one another and considerate of each other's roles, but this whole project revolves around the fact that the patient is there for the evaluation and treatment. This isn't a matter of your job being less important or anyone being equal or unequal.
She is [words that would get censored]. That is definitely mean girl. Most everything you've written about them is bona fide mean girl.
PART of the problem is that your own employer has you at each others' throats and that's nothing new AT ALL. I will come back to this, but one more important thought, first.
**The reason that many big places have developed such specific registration processes is because of a federal law referred to as EMTALA (Emergency Medical Treatment and Labor Act). I'm not sure how familiar you are with it (don't mean to insult your intelligence here), but it's a big enough deal that employers don't want even the appearance of violating it in any way. One of the major provisions of EMTALA is "examination and treatment cannot be delayed to inquire about methods of payment or insurance coverage."
This doesn't mean that registration/billing activities can never happen until treatment is complete, but it does mean that no one wants to give the appearance of delaying the treatment part of the patient's visit for anything related to payment. So hospitals generally develop specific processes about specifically when (during the patient's visit) registration staff will complete their duties. All the hospitals with which I'm familiar aren't taking any chances with interpretation, and have decided this means that at no time will the activities of their registration/billing departments delay the medical/nursing care of the patient in any way. They want it to be very clear to everyone (the other staff, the patient and the family) that collecting your money is not taking priority over this IV that you need, this medicine that you need or this test that you need.
For all these reasons, which I sincerely hope you understand are not about me or you, you simply should not be being asked to collect money and all of that while the medical/nursing staff is engaged in episodes of active patient care/treatment.
If you really like the job, here's what I would do.
I would read and research the related issues so you know you're sure of what you're talking about. Then I would go to your manager and offer to help spearhead a more coordinated effort that allows you and the nursing/medical staff to all do your jobs with fewer instances of getting in each others' ways and one that, to the extent possible, does not interrupt care in order to collect payment.
It's too bad the nurses don't have the maturity to come up with a process improvement plan related to this.
The other thing I would consider with regard to these nurses specifically is letting things cool down a little and then start trying to make some inroads. Go to the charge nurse and say you aren't happy with the registration process because it seems weird to be exchanging money while they are trying to take care of the patient (which it is weird--to almost everyone; the direct care staff, the patients and the families....hospitals get plenty of complaints about this kind of thing if they aren't careful). Let the nurses know that your manager has put a lot of pressure on you and no one has really explained anyone else's role or perspective so that you can try to work together. Tell her that you're tired of getting in their way and generally having the problem you're having. Say it kindly (which honestly is more than they deserve, but keep your goal in mind!!).
This is a problem with your hospital basically pitting roles against each other (I mean, who isn't going to hip check people out of the way when your VALUE as an employee is being judged by something so stupid as how fast you do something)? I'm being a little silly here just to lighten the mood, but it SUCKS, it downright sucks the way each of us--you, me, and the doctor--are being judged these days. Our **ONLY** hope is to try to rise above and work together despite such a degrading and unpleasant situation.
Sorry for the book but I hope it helps in some way. Let me know what you think or any questions...