Hello! My grandmother's dentist told her that she needs to have a root canal on 3 teeth.
My opinion is that she get a second opinion preferably from a holistic dentist
The pain indicates there is a problem, but the holistic dentist will determine to what extent, and advise on any needed treatment.
If he recommends removal, he will do it in a proper way. You didn't mention if the teeth had fillings in them that contain mercury, but that dentist will remove them making sure she doesn't consume any of the mercury.
The best way to clean teeth is with a water pic machine with a little 3% H202 mixed with warm water. This cleans around the teeth at the gum line, and in between the teeth.