As a non-burger, non-leaf I don't actually understand how Lauren was ever considered a libertarian. Anyway, let's get to her shitty points.
The first mistake she makes is instantly associating libertarianism (and it's "movement") with the libertarian party, something which I don't blame her for doing, since for any statist mindset like hers, ideologies are necessarily associated with political parties. The support for the libertarian party is Rothbard's worst mistake by far, as he did not understand, like Lauren, that the political route only makes sense in a short term strategy, and that the reduction of the size of the state will never happen, because the nature (or the incentive structures, if you will) of the beast is to ever expand itself. Minarchism is unethical, unsustainable and useless as a strategy. More faith in the state WILL NEVER mean a smaller state.
Her second mistake is not understanding libertarianism. Libertarianism is a theory about the law, it's about an ethical juridical system that dictates human action (which actions should be allowed or not). There's not such thing as "pure" libertarianism. You either subscribe to the idea that private property is the only rational way to solve conflicts, or not. To say that this system is not possible right now, and therefore we must continue to sustain the very same unethical system that hurts private property, is nothing but an utilitarian fallacy to throw ethics out of the window for the sake of convenience.
>hurr only Kim Jon Un believes any economic freedom is bad
Wrong. Most people in the world believe that the state should control the economy. That should be reason enough for you to stop supporting democracy or the state altogether, but that's beside the point.
The open borders vs close borders debate is a trick question for libertarians. The state shouldn't have any property whatsoever. Either "solution" guaranties that the problem won't be solved, and by problem I mean the public property problem. The only rational solution to the migration problem is to privatize every piece of land and let freedom of association (and from association) dictate who gets in your property (something that the American state prohibits, since secession itself, an integral part of freedom of association, is considered a crime). Any other solution reinforces the idea that the state should control anything at all. And the state completely relies on it's psychosocial validation to even exist. This alone should tell you how supporting the state in any way is detrimental to libertarianism.
Her points are pretty pathetic and she mostly relies on fallacies. Lauren and folks like Cantwell are what happens when you throw ethics out of the window so you can feel more comfortable and have a sense of belonging to a group. It's unfortunate that people like her have voice and influence on other folks that consider themselves libertarians.