Insufficient information to judge the merits of the question + score. The quick assumption is that she was marked off for not answering they should have the same ideas. What if she was marked off for not explaining enough or for not drawing a full set of concepts from the lesson to support her assertion? Or if that is literally the answer, she mentioned conclusion but did not mention hypothesis or theory; the rubric could be that simple.

Like:
It is better to have different ideas. Because those ideas are the input theories to the scientific process they will pursue together. The theories then inform a set of hypotheses to test. They test the hypotheses, and the one who had the idea most matching the conclusion has to buy the first round.

Again insufficient information to know, but it is one plausible explanation for the grading.