Camera and mic on or off?

Maybe you read my last question. I'm supposed to turn on my mic now and not always mute myself, but also the camera. So far I have been able to talk myself out of the fact that I'm not at home and only have an old laptop with no camera. Now she said I should use my cell phone so she can see me. Can I say anything that sounds believable? She is stubborn and says it is because of the school light.

Huhu!
You can't get expelled from school for it! ^^
Just say that your phone is low on battery (5%) and you can't find your charging cable.

She doesn't believe me