OP, what year is she in now and what grade levels is she at?
May be easier to work backwards if the goal is to meet the criteria for music scholarships - I don't know anything about the aptitude ones but we did undertake a number of auditions for the West London indies 3 years ago.
My DD sounds like a similar profile to yours. Good at music but not virtuoso level, but driven, good ear, and active in sports, dance etc.
We discussed around Y4 (G3/G4 levels on instruments) what the requirements were for scholarship applications. Instruments started in Y3, some grades missed due to ability, but, scales and technique for grade missed always covered. G5 theory was missing though (I had no clue this was a requirement for post G5 ABRSM, the school's preferred board), so she took to self learning and got it covered off quickly. The biggest hurdle to meet the application deadlines was doing G6 violin in one term for Summer Y5. She achieved a 127, low and hugely disappointing for her - a bloody marvel in my eyes, given the speed of achievement.
All of this was hugely tactical, calculated and yes, pressurised. BUT, she was up to it, knew an application added value and understood the quid pro quos' of a scholarship. Yes, she was at a school that liked to only enter children once distinctions were in sight (like your post), but once we had battled through the theory (against their wishes, I sat her independently at the time) they knew she was seriously committed to trying. They then supported her because she's proved them wrong.
DD's not sat a violin exam for 3 years now, would probably be around G8 for last 2 years, but more importantly, doesn't know (nor care), as the focus has been improving technically, and playing repertoire that doesn't require a 'what grade is this' comment. There's a modest kudos that comes with a scholarship, engages well with all school ensembles but doesn't have aspirations to make a career out of it. Is surrounded by quality musicians, some like her, some with JD backgrounds so a real mix. It's a good compromise for a kid who has interests that take time (like sports) but enables them to play an active music life too.
Long answer, sorry. In summary, yes, applications say G5/6 or equivalent (in London at least). Reality is some schools do filter like CVs, and if the prospect cohort is strong, the odds are challenging for anything below G5/6 on 1st instrument, unless unusual one (and converse). Some HoM do not look at teacher references, fact (good ones do and will take the reference as equivalent level, asking for repertoire covered). It's all so tick in the box, but if the goal is to secure an audition post passing the exam mark, then it becomes fair game from thereon. And great achievement and experience for your child.
The pass mark can be such a red herring, necessary for paper purposes but has no reflection on a child's musicality, if the exam is sat at the wrong time for that child's musical standard. Not sure if I have made sense in that statement but I know in my head what I wanted to say!