Not at all! As a smart consumer, you did the right thing. She should not have had a problem with showing the documentation & I suspect knew that she was hiding something by getting upset by your request.
No - just like all car dealers are not like this (Lexus / Ford / Honda...any kind). She was just having a bad day & you received the attitude.
Lexus has their honest and plesant dealerships/sales people as well as a few that aren't so customer oriented. My guess would be that these sales tactics are coming down from the sales manager (good cop / bad cop). I think these dealerships need to realize that there is so much competition, they really need to work harder & better for your business. Repeat business is really important for dealers, as are customer referals. This dealership just received a negative word-of-mouth post on a Lexus forum...not good for business!
I hope you enjoy your new Lexus!