She believes, contrary to many of her colleagues, that this determinism holds everywhere, even at the quantum level.
Many physicists have for the last century argued that quantum events, events involving sub-atomic particles, were indeterministic, that there was no way we could predict them because they essentially had no physical cause. One reason this view of quantum mechanics was popular was because it allowed room at the quantum level for free will.
If Superdeterminism was true, many physicists believed, there'd be no way to hold on to free will and the philosophical consequences of abandoning the notion that we are somehow free to choose are extensive, including the loss of moral obligation, human culpability, and human dignity.
Here's Egnor explaining this:
The conventional view of nature held by materialists, who deny free will, is that all acts of nature, including our human acts and beliefs, are wholly determined by the laws of nature, understood as the laws of physics. We cannot be free, they assert, because all aspects of human nature are matter, and the behavior of matter is wholly determined by physical laws.Ms. Hossenfelder is one of the latter. She thinks Superdeterminism is true and although she herself doesn't believe that we have free will, she nevertheless doesn't think that Superdeterminism really has anything to do with whether we are or are not free.
There is no “room” for free will.
It’s noteworthy that physicists who have studied determinism in nature (specifically, in quantum mechanics) have for the most part rejected this deterministic view [at the quantum level] and implicitly (if not explicitly) endorsed the reality of free will. There are two reasons for this.
First, experiments that have followed from the research done by Irish physicist John Bell (1928–1990) in the 1970s have shown that determinism on a local [or quantum] level is not true. The theory and the experiments are subtle, but suffice to say, detailed and quite rigorous experiments have shown that the outcomes of quantum processes are not determined locally.
That is, there’s nothing “baked in” inanimate matter that determines the outcome of the quantum measurement. Nature is not locally deterministic.
The second reason that physicists have rejected determinism relates to the theory of Superdeterminism. Superdeterminism posits that, while inanimate matter is not locally determined, the entire universe — including the thoughts and actions of the experimenters who are investigating nature — is determined as a whole.
The experiments based on Bell’s theorem have disproven local determinism but they do not disprove Superdeterminism.
The problem with Superdeterminism from the perspective of most physicists is that it seems to invalidate the process of science itself. That is, if the scientists’ own thoughts, ideas, and judgments are just as determined as the behavior of inanimate matter, then science itself has no claim to seek or find the truth.
...If all of nature is an enormous robot, then it makes no sense to claim that tiny parts of the robot are seeking or have found the truth. Because Superdeterminism seems to obviate the very scientific method used to investigate it, physicists have generally rejected Superdeterminism.
Recently, however, several physicists have suggested that Superdeterminism is a quite plausible way of solving the measurement problem in quantum physics so it seems to be having a bit of a resurgence.
Here's her video on the subject: Egnor agrees with Superdeterminism but also believes we are free to choose. He reconciles Superdeterminism and free will by positing a "block" universe in which past, present and future all exist simultaneously. This idea, as counterintuitive as it may seem, is actually a consequence of Einstein's theory of Special Relativity.
I'm not sure Egnor's argument rescues free will from Superdeterminism, but you can decide for yourself by reading his argument at the link.