The inventors of Infra-Red Remote Control watches allowed the disruption of many an Apaches video.
Adjust the volume.
Hopefully, the television will be before on-screen displays of the volume, so it would just seem like a mechanical glitch. The teacher will be concerned, but not enough to stop the video.
Pause. Resume.
Timing is everything. First, quickly stop-start the video to let everyone know something is amiss. The second time, not too long after the first, and only resume when the teacher gets out of her chair, leaving her hovering in mid-air, unsure which way to go. Then leave it for a minute or two, until everyone thinks it's working again, then pause and leave it until she actually gets to the video before you hit play. Then hit pause the second she sits down. When she gets back to the video, move to the next stage.
Fast Forward / Rewind
Convince the teacher that something is seriously wrong by pressing something on your watch immediately after she presses something on the video. She presses play? Hit rewind. Continue until she is hopelessly flustered, and fetches another, more male, teacher.
Resume Normal Service
When the other teacher is in, you obviously let the video run normally. You should also complain that this video on the Bayeux Tapestry is really interesting, and it's frustrating that you can't seem to watch it in the manner the programme makers intended. The other teacher will leave, perhaps rolling his eyes at the flapping woman in his wake.
Tear Her Soul Apart
No mercy. The second he has left the door, bombard the video with everything you've got. The look of pained helplessness and growing panic on her face will inspire sympathy in only the gayest of children.