Being asked to comment on an unseen poem after just ten mins is a gift of an interview task because you would not be expected to know all the possible historical contexts or famous critical reviews of the piece. They would have been expecting her to comment on what she could actually see on the page, e.g. form, structure, metre, tone, phrasing, choice of words, subject, any invocation of myths or folklore, meaning, etc etc. There's so much she should have just pounced on! When I was at school that's what we did all the time in English Literature classes, we were often given photocopies of random poems or chapters to pick apart in order to discuss. In the discussions the teachers wanted us to explain what we could observe and infer from the text as a standalone piece. Of course for other tasks we learned how to analyse texts in contexts of history, society, critical review, but analysing extracts was definitely something we did a lot. I went to an inner city comprehensive school, which at that time had no successful Oxbridge students for years! I'm very surprised if Ruby wasn't similarly shown how to pick apart unseen poems.
What the Oxford interviewers probably wanted to see was can the potential student demonstrating the ability come up with things to discuss and explore, from practically no preparation. They wanted analytical skills being applied, not regurgitation skills.