I misunderstood. Char's been able to control a monitor for a while. It was first mentioned during Haruto's fight with the asshole noble, when he uses beams of light to keep things family friendly for her. She also has interacted with the professor as Weisse Owl without Haruto even being present or seemingly aware it's happened.
I don't think he's ever explained giving her a device, but it was probably during the timeskip between collaring the queen and being told he was going to school.