AJ, what's up. Unfortunately you're going to find a lot of nit pickers and Randroids on this forums, but alas there are many good posters. Whilst it is true Rand used her own terminology, most people recognize the resemblance of the non aggression principle with Rand's non initiation of force principle, and Rands right to life with the Lockean phrasing of self ownership and property rights. I think these are literally the same thing.
I also think that she is right, along with Rothbard and others, to criticize many other libertarians because they do not ground the axioms of libertarianism in a rational ethics. And many are just plain kooky and weird, but hey that applies doubly to many objectivists.
So I celebrate Rand's unique achievement in her melding of a neo-Aristotelian ethics of virtue with libertarian political philosophy. I think these two both jointly supplement each other, and provide the best case for either.
Also note that Rand didn't have one argument for an NAP, one for self ownership, one for propert rights, etc, but since she believed in the Greek "unity of virtue" concept, her argument for one constitutes her argument for all.
And there's not just one single arguement for grounding the principle of rights, it is more a web of arguments, different strands depending on how you analyze different aspects of man's nature.
There is the aforementioned aspect of her philosophical psychology, that she often posits that reason has to be an independent judgment, and that one cannot act on the basis of reason to the extent one is subjected to force, and that one needs moral autonomy to think and act independently.
There is the trader principle, that is that living in a society can be of advantage to you, but only on certain conditions, eg., that you have the opportunity to trade, and that aggression is not a dependable and reliable means of obtaining values and so forth.
There is her observation that sustaining human life is impossible without appropriating and producing material values and one cannot reliably acquire or produce values for exclusive control under the threat of coercion, and that leads to homesteading and contractual trade and so forth.
She gives an argument based on the metaphysical equality of all men, eg., that after we have established a substantive ethics of long term happiness and well being, that if you recognize the requirements of yourself being free to act on your own reason and values, and that is a constitutive part of your own flourishing, then that commits you to valuing the same right of others to promote their well being (and this is part of her argument for the virtue of justice.)
It is in this sense a type of natural law argument, that reason shows us various aspects of man's nature has certain requirements for being able to achieve happiness and success in a social context, and that all of these things point to a thoroughly robust non aggression principle on egoistic grounds.