vinnygal I have experience of having a DC suspended for facebook activity, as well as several meetings with heads, etc. that were unpleasant in that I had to listen to things about my child that I wished were not true.
ime, one thing that undermines them slightly when they are trying to tell you how bad your DC is, is if you can tell them how much you like the school in general, how happy your DC is to be there, how much they have learned, etc.
In your case, are there some subjects where your DD is doing well? If so, maybe you could start off with complimenting the school regarding the other subjects.
It will be useful to you if you can be concilatory and apologetic (ie, DD was foolish, shouldn't have done that, etc.) regarding what DD did.
You can also be demanding regarding seeing the policies on suspension, etc.
You could at some point mention that you are " "surprised" that DD got an "E" for sociology, which she likes" (if that is true). What is the school doing to support the sociology teacher who got "Es" for the whole class?
Sociology must be a really hard subject to know what is expected in the exam - if the teacher has a different view to the examiner, this could be a difference of two grades.
Final tip: can you take a friend/parent/DP with you? I once had a four-on-one, and it took some time for me to recover.
In any case, DD will be out of that school within a few months, and your objective in the discussion tomorrow is to minimise the disruption to her and to maximise the chances of her doing well overall.