The judge was aware of the warrant and ensured the defendant remained in private areas so they could get out of the building.
The FBI's argument is that her actions were unusual (a defendant being allowed into juror's corridors is highly unusual) and were only being taken explicitly to assist in evading ICE.
As we've heard from many lawyers recently regarding ICE... You are not required to participate and assist. However, you can't take additional actions to directly interfere. Even loudly shouting "WHY IS ICE HERE?" is dangerous (you probably should shout a more generic police concern, like 'hey, police, is there a criminal nearby? should i hide?'
That's a general applicable law that prevents anyone - judge or not - from interfering with an apprehension.
If they are arresting people using them and judges are recognizing them, they are real and the people demanding an arrest warrant are the sovereign citizen-tier people screaming at the sky wishing there was a different reality.
It is both rational and legal to insist that law enforcement stay within the bounds of the authority the specific type warrant they obtained. ICE civil warrants grant different authority than every-day federal arrest warrants. That ICE is abusing that authority is no reason to capitulate to it.
Their only real purpose is fooling the gullible into confusing them for real warrants.
Interfering with an ICE apprehension is illegal. That's what this judge did, which is why the FBI arrested her.