Hannah – you have come to the right place to ask these questions. Teachers and careers advisers generally have zero knowledge of what's involved in becoming a commercial pilot – apart from perhaps entry requirements for the occasional sponsorship schemes.
I did A-level physics, and found the experience very useful when studying for my ATPL theory exams. It's not vital, and you could certainly get by without it – just nice to have under your belt. I failed A-level maths, which matters not, as the maths you'll use in the flight deck is barely GCSE level. Seriously – simple adding and subtracting, and the three times table – that's about it. In fact, most of the technical / academic knowledge required is around GCSE level. Believe it or not, of the subjects you mention, French would probably be the most practical use in everyday airline operations. Many of us fly into regional French airfields where the ground staff speak very limited English, not to mention half your passengers who can't understand a word. And French is most certainly an aviation language, and is widely used on the radio across the Channel. Controllers will speak English to non French pilots, but can and will converse in French with their countrymen. For self preservation as much as anything else, it's nice to know the French for "takeoff" and "land" when you're about to taxy across an active runway at Paris CDG . . .
As others have said, the best bet is to choose subjects you enjoy and are likely to do well at. When you're starting your career, without much life or work experience to talk about, academic grades are one of the few ways of differentiating between CVs.
And as for laughing at the idea of a 'girl' learning to fly – yeah, right. My female PPL instructor was (is) one of the most professional instructors I have ever met. Nearly 10% of the pilots at my airline are women, and if you're good enough to jump all the hoops and get through training, you're good enough to fly an airliner. End of story.
Best of luck with the A-levels.