act of War, and thus constitutes Treason, then she cannot be arrested for doing so, and cannot be arrested while going to or coming from a session at the capitol. The Constitution forbids it. (there is also the option to charge her with a Felony or Breach of the Peace perhaps)
They shall in all Cases, except Treason, Felony and Breach of the Peace, be privileged from Arrest during their Attendance at the Session of their respective Houses, and in going to and returning from the same; and for any Speech or Debate in either House, they shall not be questioned in any other Place.
The reason the Framers put this provision in, was because King George would repeatedly render State legislatures useless and unable to obtain a quorum by arresting various members and preventing them from attending their sessions. He would also draw up trumped up charges on them if they cast votes or introduced measures he didn't like.
We need to keep this provision, however, I could see easily how introducing a disarmament measure would constitute "breach of the peace." Though, good luck finding anyone to issue an arrest warrant on that basis.