I know someone who lost 2 fingers on his right/dominant hand at work and got lawyers involved. He ended up with only $20k for his injury but the lawyer collected another $10k. If he had just worked with his employer he would have done better- as soon as the lawyer got involved they circled the wagons and any offers of settlement disappeared. A jury agreed that the employer was wrong but that the injury didn't have that much value. Most of us would probably disagree with that I would think. If you go this route then you may even end up with nothing if the jury finds for the defendant. I think if you handle this diplomatically then you can reach a good conclusion for all involved. You can even get a mediator if you want to ensure that it is all done on the up and up. Just keep away from lawyers- it will spiral out of control and you will not benefit as a result. They are looking out for easy money for themselves and don't care about you.
There are good lawyers and bad lawyers. Just like there are good doctors and bad doctors. Many bad doctors are kept from continuing to practice medicine in a negligent fashion, and many harmful products are off the shelves, because there are lawyers to file lawsuits that *should* be filed. Not all cases go to a jury, in fact most don't - many times, no lawsuit is even filed, attorneys settle many cases without filing.
Since the OP has been offered no compensation, other than no charge for the second root canal, the question is what course of action will get her compensated for the future dental care she may need - even if you don't agree that she is entitled to anything for the pain and inconvenience.
If someone is injured on my property, I have insurance to cover them. It wouldn't destroy me financially if they were to pursue and claim and to collect - that's why I carry insurance. Medical cases can be complex because people often develop future problems, as many have pointed out here. It's a disservice to paint all lawyers with the same brush.
It's certainly your right to never use one and to negotiate for yourself no matter the circumstances. But each case is different. Giving anecdotal information on one case as evidence to support your advice to stay away from all lawyers - because you believe they are all out for easy money, don't care about their clients, and don't get their clients funds to pay for additional future care as a result - is misleading.