conditional 2 and 3 confusion

[magdalena]

hi! I have a question on conditionals. imaginary sityation: two girls are talking about problem with math teacher one of them had when she was a child.

And here comes a sentence which confuses me: " Oh really? And your parents did nothing about it? If you had been my child I would have demanded that such irresponsible teacher be fired" .

Sick! I thought, that, since she (obviously) is not a parent of her girlfiend the second coditional would be correct "If you were my child I would demand..."

Since this is one choice excercise mine would be a wrong answer. Why?

[Tdol]

You could use a mixed conditional there:
I you were my child, I would have demanded...

The second half must be in third conditional to show that the events were in the past, and to use 'would demand' is wrong'. The first part could be in either the second (which shows that she isn't and never will be the parent) or the third because it is referring to past incidents.