At the time of the quarantine, that was unknown and NOT PROVEN.
She failed to abide by the self quarantine, and acted as if the rules did not apply to her.
And at that point, nobody knew if she did or didn't.
You have the timeline backwards. You're right that she acted irresponsibly once she was in Maine, under self-quarantine. The mandatory quarantine came BEFORE the self-quarantine. She was placed in mandatory quarantine (in the tent) before she ever did ANYTHING. And that is the quarantine she is suing Christie over.