Having the state police arrest people without an explanation is in and of itself evil. Citizen or no.
So yeah, I'm going to make the worst assumption about why they are doing this because they should have to explain themselves. We still, presumably, live in a democracy where the state is accountable to the people. Letting the state police remove civil rights for opaque reasons should always be treated as them doing it for the worst possible reasons.
But let's say for the sake of argument that no explanation was provided, even privately to her and her attorney. I would agree that's bad, even if it's legal in the case of visa holders.
But why should that cause us to make assumptions about the reason? And if we're going to make assumptions, why this particular one? Why not assume she was detained because an officer didn't like the color of her shoes?