If extended writing is not her strong point, history would be a surprising uni choice (or even A level).
What grade is likely in maths GCSE? Not much point taking it and getting a lower grade than in something else – what I mean is, it opens doors to science degrees but not so much if you get a C/D.
The trouble is IMHO if you genuinely want to keep options open at A level, it’s really tricky. DD took three subjects which open doors to studying those subjects at uni (Eng lit, geog, MFL) but even then she closed loads of other doors – biology, physics, maths, chemistry, engineering, medicine, dental, vet med, music, art, DT, classics – you get my point I am sure.
Actually a number of unis (inc Leeds for example IIRC) don't require history A level for the degree. Otoh if you love history that much, surely you would want to take the A level.
For medical subjects biology and chemistry are the best options; also good for psych. Psychology itself is not needed for a psych degree tho it will give an idea of the content. It doesn't in itself keep any options open tho.
I guess my list, based on your OP, would be: bio, chem, maths (caveat: as long as GCSE is 8+), history (caveat: concern about not liking writing essays). MFL if she takes one (needed for MFL at uni)? Geography (if she takes that at GCSE)?
She should only take three ideally. Bio, chem, history would keep both medical and history/humanities options open.
ETA: I took so long to write that that I have x posted. I actually disagree re psychology being rare – IME it is a very popular A level and frequently offered in sixth forms local to me at any rate. Lots of ppl take it and then drop it tho as it is much duller than they thought.
It's not unusual for medics to take history actually as it shows breadth – but I see she is not keen on med anyway. Maths supports the other sciences better than history tbh. You don't say her likely GCSE grade but that is key.