I agree completely. I believe I should have the right to carry and defend myself in any state in the Union.
However, we both know that realistically and unfortunately that isn't the way it actually works. If I want to stay out of legal trouble, therefore, I have the responsibility to know what the laws are wherever I'm going. That information is readily available on the internet; anyone traveling would do well to access it and become familiar before traveling.
I agree with "should" but about 1/3 of the US population lives in the indigo-blue states that restrict firearm ownership to a greater or lesser degree. The SC has ruled that states can restrict firearm ownership.
One big reason that the SC ruled District of Columbia v. Heller is that DC is not a state.
Still, it's hard to believe that CCW course in Tennessee wouldn't have mentioned anything about laws in other states. It was pretty dumb to bring a pistol into NYC and pretty naive to think that cops are your friends. She has my sympathy but she should have thought about it for a second or two.
I don't think NYC's Sullivan law is going to change unless NYC residents want it to change, and they haven't wanted it to change for the last 100 years.