It is illogical beyond all get-out to say Pelosi can obstruct Congress, because she can be voted out at any time if House Democrats are unsatisfied with her leadership.
If she somehow fails to transmit the Articles of Impeachment to the Senate (which she is not constitutionally required to do), then House Democrats can do just this, if they want to.
And: it is not a violation of the Constitution for the leader of the House and the leader of the Senate to negotiate about process.