Schielle1 - I know you are trying to do the right thing in getting a safety issue resolved for your mother, being the primary driver. I agree that should be the primary concern.
NPF = No Problem Found, frequently this is the diagnosis by service departments when they cannot (or don't want to) reproduce the problem reported.
And to clarify the point (since you were wondering what my point was), ideally the problem should have been reported and recorded at least once during the warranty period, even if the the service department in question failed to acknowledge the defect. It would just give your post-warranty claim more weight (and documents the fact that a problem was observed by owner during the warranty period, and remains unresolved). Consider taking it to another Lexus dealership, especially since the warranty just recently expired. If the problem is obvious, they could very possibly acknowledge the problem and honor the warranty.
Of course, when I see comments like "Actually, you sound like Bellevue dealership's representative" I wonder if you have developed a somewhat sour relationship with that dealership service rep., so trying another might be considered.... I apologize for having to point this out....
Best of luck, many of us have had productive exchanges with Lexus dealership service departments.