JKL33

1) I would not perform any wastes with this person unless I could verify the whole process and account for every piece of information that is being attested in a co-signor situation. I would try very hard not to put my name on anything that had anything to do with her.
2) In real time, *first and foremost*, I would have carefully assessed my patient and if he was not arousable or had significantly decreased LOC, I would have sent him to the ED.
3) I would have immediately addressed the information from the 2nd coworker by informing her that she must report it. I would tell her I'm sending my patient to the ED and she would be very wise to report what she knows.
You don't have the proof you need right now. Just the same, this is nothing to mess around with and you have to be prudent. You can't just sit around feeling all shocked that someone (allegedly) might do something like this.
I would look for a new job yesterday. That's just me. I wouldn't screw around with this situation in which the most likely thing would be that the patient's primary nurse would be blamed for what happens with a patient. You have zero defense against any accusations that could arise subsequent to another nurse causing your patient to become obtunded by medicating him/her with something off the record.
In the back of your mind you must be aware that Nurse #2 could've said something just to stir a pot. As you know, it's not at all uncommon for an elderly narcotic-naive patient to be zonked by a single pain pill or two. Just the same, this scenario is one too many wild-cards for my personal comfort.

1. You need to find a way to stop caring about this. Pronto. You need to stop feeling uncomfortable over other people's inappropriate behavior. I'm not chastising you--I did it for a long time, too. But really, how silly is it to watch someone else be inappropriate in one way or another, yet you come out as the one feeling embarrassed, afraid, upset, etc? THEY certainly aren't worried about how they look, and if anyone should feel embarrassed, etc.--its them.
The less you care, the less power they have.
They are able to affect and to some extent control your behavior **only** because you care about something that you should not care about.
Let this person go whine and complain and accuse you of not being able to handle things all she wants. The more she does it, the more SHE displays that she is the one with the problem, especially when her complaints are about anyone/everyone, not just you. If your manager does ask about you it (kind of unlikely), convey that you are unaware what s/he might be talking about. IN FEW WORDS. As in, "huh--not sure."  Or, "Sorry, not sure what she is upset about." Then don't stand there and continue to be engaged in hearing about petty complaints.
Nope. Not concerning for you. Go concentrate on what's important, which is taking good care of patients.
I hope you will continue to work on this. Re-read this post, I think it is solid advice or I wouldn't have written it.
You just have to believe it.

I don't know, but I wouldn't work in a place where those I am supervising get off scot-free when they leave the facility for hours. I can almost guarantee you there is more badness you just don't know about yet. Any place where someone caring for patients feels free to just walk off the job for however long they want is a place that has BIG problems.

Because that is not how the ED works. The overarching goal there is to safely dispo patients, meaning get them out of the ED. They are either staying or going. In the case of staying, as soon as that is decided the goal is to make it happen so that the bed can be freed up for the next patient. Whatever is in progress at that time is continued in the next place. There are plenty of situations where ED patients have orders for things that might be necessary but do not need to get done in order to figure out whether the patient is staying or going, and/or do not facilitate them getting there. So they are lower priority.
I would guess that what was said was more like, "responsible for seeing that they are (or have been) carried out appropriately." There is no way one nurse can personally carry out every single order.
With that said, I agree with your general concern on this one.
There is a reason that an RN needs to sign their name to something. Acknowledging an order is the same as taking nursing responsibility to see that it gets done or has been done. Though employers might like to make us feel like "acknowledging" is just a box-checking type of formality, nah, it's taking responsibility. In my opinion the responsibility for acknowledging should fall to the person who had a fair likelihood of having the opportunity to at least do basic double-checking and see that things are in order.
ETA: You could facilitate a discussion about this by just asking "so when we are acknowledging orders, what is the purpose of that? What are we attesting to? That we "saw" the orders? That they are appropriate for the patient? That they got done? That we carried them out ourselves?" Get an answer then you can decide how to handle. You should decide how to handle based on the answers you get; not on whether someone on the previous or next shift is going to huff and puff about it.

As best I can guess: This technically has nothing to do with HIPAA. You, the one who would be disclosing information, are not a HIPAA covered entity. In addition, you would not be naming any references without the individuals' permission, and could even have them sign some kind of statement to that effect. Even further, as you said--the references are not the patients.
That said, it's still sticky because, as you have found out, people freak out about HIPAA and think the silliest things have something to do with HIPAA--just read some of the inquiries in this sub-forum! There's also the matter of appearances--another thing people get high and mighty about; too many people love to question others' "ethics" when they don't even stop to consider facts like the ones in your scenario.
I'm nobody, so this really means nothing and you should do what you think makes the most sense, but I would consider a couple of options if it were me:
1. Tell the recruiter that you can provide references from clients with whom you've worked, period. Leave it at that.
2. Or just fill out the app with the names of the clients who have consented to act as references
The hiring entity will know that you can't provide what they're asking for if/when they review your employment history
Anyway, good luck, hope it works out ~

Remember that you don't have to entertain multiple lines of attack. Even if the patient has designated two or more people who are authorized to receive information you certainly can ask one of them to act as a point person to relay messages to you and to relay your info to the others as appropriate.
You should not. If you blew off the patient's pain perceptions and declined to attempt an intervention you would have something to feel guilty about. I  feel like using a "stern" voice on this matter because your guilt reaction is very unhealthy. You can't assume that you should feel guilty (and that shouldn't be your automatic emotion) just because someone is displeased about something. Instead, practice staying in a neutral/professional problem-solving mode. Just hear what is being said without taking it personally (even if they are using personally-aimed language) and then attempt to intervene as appropriate (this latter part you did do). 
Remember also to not fall into what I call spinning mode where you are just reacting to every comment/complaint. As an example (no harsh critique intended here ?) - they started at one point mentioning the IV site. Well, is it working properly or not? If it isn't, start another one. If it is, demonstrate that you have carefully assessed it and then declare that it is working properly. The end. Not: Okay well let's do some kind of something because they have complained. That can be a trap because if nothing is wrong to begin with then your intervention can also be faulted, KWIM?
Bottom line, everything's okay here. Don't lose sleep over this. ??