Child psych 101

I'm trained in, and a firm believer in, a parenting program call Parenting With Love & Logic.  Three keys parts of its philosophy are:
1) Insisting that children own their own problems and don't make them a problem for anyone else.  Therefore, my child has the right to be upset about something, that's ok, it's her problem; but if I then have to listen to her crying and screaming, she's creating a problem for me, which is not ok.
2) I try not to give orders I can't enforce, because if/when the child refuses, my words mean nothing and I lose all credibility.
3) Tantrums, and many other misbehaviors, are usually a bid for attention, or a means of manipulation, which if even occasionally successful, will be used again, and again, and again, and again.
This is very sound theory and, when applied appropriately, should work with most kids.

So, I don't tell my child not to have a fit (because I can't control that, and it will certainly backfire), I tell her where she needs to be if she chooses to have the fit, namely away from me, where it won't hassle my ears and will not be awarded attention.  In her room.

Love & Logic suggests asking the child if she will need the door open or closed, theorizing that the child who feels in control of this option will be less likely to resist it.  If the child shows by his behavior that he cannot handle having the door open, we show that we read his signs by closing it for him.  Some kids will actually leave the door alone.  Some will test the parent by peeking out, but give up when they see the parent patiently waiting outside.  The whole idea is for the child to eventually learn "If I choose unacceptable behavior, I will have to spend time alone in my room. That's not very much fun and I may miss out on something".  Later, when warned, the child will decide to change their behavior instead,  or if time-out is necessary, they have time to calm down before rejoining the family.  As long as parents make sure the behavior doesn't pays off for the child, he'll soon give it up as useless.

But what if she doesn't?  What if you do everything 'right' and it only makes it worse?  'The child is stubborn, don't give in, be consistent.'  Ok, but where do you draw the line?