After the huge shoot out in the hallway there’s no denying her involvement. Captain Antilles and Princess Leia are both just delaying Vader for as long as possible, hoping Artoo can get away and find Obi-Wan. As for the transmissions being beamed. We don’t know if Vader saw that soldier hand off that data tape. His mission as mandated by Tarkin is to mop up the space battle and prevent ships from escaping. So he could have been on his way to try to stop the Tantive from launching. Alternatively, as the Tantive was docked inside of Raddus’ ship, Vader could consider them both just one vessel and as we saw, the plans were beamed up in about four or five chunks simultaneously.