I would immediately say that with such low numbers you cannot possible surmise if one school better than the other. It maybe more useful if you knew how many children went for the oxbridgea nd how many qualified, so if of 10 girls only 1 managed it that would be more meaningful, but with such low numbers an overall how many is not very useful.
If 10 girls got offers and only one managed it would really show that something had gone wrong with the A levels at that school. It would demonstrate to me some very talented girls had failed to get their A* grades and for the Arts courses at Oxford their A grades. It would shock me if a good school didn't react in such circumstances and would be a strong warning sign in the same way the number of girls who made their first university offers or the types of courses they got onto and into which universities.
My eldest dd has a poster on the wall in her room at university which states" Don't tell me the sky is the limit when there are footsteps on the moon." There is nothing wrong in reaching for excellence in any field of life even if you don't get to its very limits.