The question said: 'Identify the central idea of each extract and analyse how that idea is conveyed.' If she identified the central idea of the text in its entirety and then chose techniques from throughout the text which illustrate how it was conveyed, she's answered it wrong and it would be perfectly reasonable to bring that up with the head teacher. If, however, she chose multiple extracts, identified the central idea of each of these extacts and then demonstrated how they were all conveyed she's done nothing wrong. In the second example, she's just answered the question in more depth than was specified. However it seems that she's done the first, which you are correct in stating is wrong. She hasn't answered the question as she's dealt with the central idea of the entire text, not the central idea of the extracts as was specified. If that's the case there would be nothing wrong with talking to the marker or head teacher about it. Just make sure you have all of your facts right first so you don't look like an idiot if she just chose to deal with multiple extracts.
If you even mention the 'she made quotes up' part though, it will lessen the extent to which your valid arguments are taken seriously. You don't have too much ground for reproach there OP
(also, +1 to pretty much everything absolutezero said).