I used to get this. If she was shirty about something I would always get a phone call sometime to pick her up from the sick bay. I ended up refusing too.

I also got the moving out at 16thing. I took a tactic other than telling her she couldn't, mainly becuase I knew I couldn't stop her. She brought it up in a councelling session and myself and the councellor, asked how she planned to do it. "Friends house" - what if they don't have room? "I dunno" How will you pay the bills? etc etc

When she would scream that she was moving as soon she could I would just say - I wish you wouldn't but if you feel you have to there isn't much I can do is there? It took the wind right out of her sails and made her think a little. It's also much better for the blood pressure

I'm the non hysterical times when we could talk I would bring it up and explain how expensive it would be for her and that I was happy for her to stay, that I would provide for her when she was at high school. I expected a small amount of board when she got to university. So basically I'd discuss it in an adult manner so she felt listened to - and in the same way I would if one of her friends wanted to discuss moving out.