Hi OP as others have said, there is no way we can answer this question in any meaningful way tbh.
It depends on so much. Was it an actual A level exam question? Was it sat under exam conditions and marked according to the mark scheme? At this stage of year 12 I would be surprised if it was tbh as 75% on an A level question would be pretty impressive after just half a term.
In 2024 for AQA history a mark of 75%, 150 out of 200, would have gained you an A. But you can see that for yourself I am sure. That figure will vary year by year (though not that much tbf, as long as the Covid years are mainly discounted). Was it really half the A level exams in total tho? Seems unlikely. If it was a single question then the figure is much less signiicant.
If I set a candidate in early year 12 an A level exam question and got them to do it in class in exam conditions in my subject (MFL) I would be amazed if they achieved 75% tbh, which is why I suspect i may be an easier question, or they may have had support in class, or been set it for HW.
Either way we can’t tell you. But I imagine the college or her teacher can. Your DD needs to ask if she wants to know; but IMHO a working grade after half a term is fairly meaningless.
Just to offer another example of what I mean, DS2 had a maths test about this time in year 12; he scored IIC 45/96. Not great? But apart from a couple of maths whizz mates who got 75 and 93, his was one of the highest scores. One student scored 6. One scored 0. It all depends on context.
BTW 1200 students in a year? That's huge! The biggest sixth form college local to me has about 1800 students across two years; most school sixth forms have about 200-400 students. I cannot believe you are not allowed to email – but really it is up to your DD to chase this up if she wants to. Why is it so important to know the grade?