That is true though! Of course they all need to keep working hard.
That's the issue though, when staff mislead students (however unintentionally) it can affect their approach to their studies.
If I tell a pupil that their performance on a 2022 paper is a B but was an A in 2017, then I'm misleading them. An A in 2017 is different to an A in 2022 because they're different cohorts sitting different papers. The grade boundaries are different for a reason. It isn't luck of the draw.
If I'm not clear to my student that the reason why the raw mark would have been an A in 2017, but a B in 2022, is because the whole cohort performed lower in 2017, then I'm misleading them.
They can, and do in my experience, leave that conversation with misconceptions which for some students affects their approach to study.
Which is more useful for a student to go away thinking:
"I got a B and want an A but it's ok because in 2017 I'd have got an A so if I get lucky on the boundaries then I'll get my A. I'll focus on my other subjects/don't need to worry too much"
Or
"I got a B and want an A. The boundaries change each year, so if I'm serious about getting an A I need to move my position up in the bell curve so I can maximise the chance of being the right side of the cut off"
I've seen both FWIW.
Your DC sounds very motivated with a supportive parent so isn't as likely to get tripped up as she's probably going to continue working hard, but in my experience unintentional clumsiness when talking about grades does trip some students up.