"That is my next move, however being the scum of the earth that they are (only 1 in custody) I'm not sure what I'd sue for?"
YOU don't sue anyone. Your daughter is the only person with standing to sue, and she's an adult. All you can do is help her find a personal injury lawyer. Whether the persons who beat her up have income and assets sufficient to justify the cost of suing is something we obviously can't know.
"Why is it that the bar can't be held liable for the damage?"
No one said the bar couldn't be held liable. We merely answered your question about such establishments having a duty to "ensure" their customers' safety.
The general rule of American tort law is that persons are liable for their own conduct, but are not GENERALLY liable for the conduct of others. Here, your daughter wasn't beaten up by bar employees. Rather, she was beaten up by other patrons. That being the case, we start with the premise that the bar isn't liable, and it's up to the person making the claim to come up with a reason why the bar should be liable for the criminal conduct of some third persons.
Nothing in your initial post suggested any basis why the bar should be liable, but you've now given us some more facts to go on.
"Especially if they noticed some kind of conflict before the incident?"
I assume "they" refers to employees of the bar. That may establish that the bar had some duty to do something. What that duty might have been depends on what "some kind of conflict" means, when it was noticed, and who noticed it.
"One bartender stated that "something" (conflict) occurred right before they exited (at her request)"
I don't know whom you're referring to with the pronouns "they" and "her" in this sentence, and, again, "something" is ambiguous. However, if the assault on your daughter occurred OUTSIDE the bar, that may change the analysis quite a bit -- particularly if the "her" in the above sentence refers to the bartender, and you're saying that the bartender requested that the persons who assaulted your daughter leave the bar. That alone may discharge any duty the bar may have had.
"the OWNER stated he (they) knew nothing, and didn't want to get involved."
When did he say this? At what point in time did he "know nothing"? And what does "he (they)" mean?
As you can see, this is a VERY fact-intensive inquiry. That's why I previously suggested that your daughter consult with a personal injury lawyer when she is able. A lawyer can review the police report (I assume there was one) and any witness statements that may have been taken, and also speak with some of the witnesses. Only when a lawyer has fully investigated the available facts would it be proper to opine about a possible claim against the bar.