What damages and/or losses did the client incur as a result of the supposed missed cracked waste lines during inspection? Whether you missed the cracked lines or not, you did not cause damage to the lines. The lines would need to be replaced regardless of the inspection. Was her crawl space contaminated with waste water? You possibly could be held responsible for cleanup or other damages due to the waste lines failing.

I agree that the client should have called you as soon as the condition was found. Even if it was an emergency, it would have been preferrable to be notified immediately after the call to the plumber.

Besides the X-ray vision, can't-kick-holes-in-walls things, I tell the client right up front that I am not perfect. Any one inspector will, in all probablity, not see something that another inspector would find if he came in right behind. And, I would probably have something listed that the other inspector would not see.