I haven’t watched the whole video, but I’ve read her making similar remarks before. I think she is just referring to the success of modern physics in general. It is a classic reductionist statement, as is evident here (emphases mine):
These deterministic laws of nature apply to you and your brain because you are made of particles, and what happens with you is a consequence of what happens with those particles. A lot of people seem to think this is a philosophical position. They call it “materialism” or “reductionism” and think that giving it a name that ends on –ism is an excuse to not believe it. Well, of course you can insist to just not believe reductionism is correct. But this is denying scientific evidence. We do not guess, we know that brains are made of particles. And we do not guess, we know, that we can derive from the laws for the constituents what the whole object does. If you make a claim to the contrary, you are contradicting well-established science. I can’t prevent you from denying scientific evidence, but I can tell you that this way you will never understand how the universe really works.
Of course, even if one is a reductionist, anyone who has read even a little bit on the philosophy of science on reductionism would see that the above statement is incredibly simplistic and naive. Non-reductionists are not simply “denying scientific evidence”. Rather there is a debate on the precise philosophical implications of the scientific evidence.
And of course there has also been a centuries-long debate on what free will is, as we’ve seen in this and related threads. I skimmed through Sabine’s blog post and I am not very interested to engage about it, since it doesn’t seem to be aware of the deep philosophical literature on the subject. It reminds me of 2000s-era, anti-intellectual New Atheism which ran roughshod over centuries of careful philosophical debate by claiming “science” and “Courtier’s reply”.
You can also see one of her posts last week where Sabine talks about these laws of physics (Sabine Hossenfelder: Backreaction: What are Differential Equations and how do they work?). As you can see she doesn’t really invoke any particular experiment or discovery, just the general success of physics in predicting natural phenomena and using that to make a literally Laplacian argument for determinism. Honestly, even past discussions on determinism and physics on this forum (including several trained physicists) have been more illuminating and interesting: Predictability Problems in Physics.