I would try to diffuse the situation and look at the nails to see if there are signs of abuse. IF there is (and there probably is) I would say that you cannot comment on what the previous tech used.
As far as fixing them, do you have repairs included in new full sets or do you have your menu showing a charge per repair?
I usually include one repair per full set if its *not* because of my workmanship, no questions asked. If its my bad, I repair it free. Doesnt' happen anymore (did a few time though when I started in the dark ages...)
If this particular client is a nail biter or you can see signs of stress (using her nails as tools) gently, calmly (but NOT patronisingly) explain that her that perhaps you need to reduce the length to see if perhaps that was the problem. And make sure there is NOTHING that that would entice her to pick (if a nailbiter).
If she comes back after you do this and its abuse, I'd tell her flat out. She sounds like she is looking for something for nothing but being this is a service business, you have to find the balance between being firm and considerate.
And if you don't have a repair policy, get one ASAP. You don't want to be dealing with this on a regular basis.
HTH's
Nancy