Can't really agree re eng lit comparison tbh.
French A level (assuming AQA but in fact the specs don't vary that much) involves studying one French book (Eng lit even at GCSE is rather more than that) and one French film. They will have to write one essay on each in French. I would agree approx high level GCSE Eng lit in terms of analysis (tho obvs the Fr language scores marks too). This is worth 80 marks out of 400.
Then there is a speaking paper with a topic card plus an individual research project (on anything relating to France or French culture such as another film, a football team, a specific topic). Speaking paper is worth 120 marks; then the reading, listening and writing paper which examines language skills and is by far the most important (marks for this are doubled - again I am speaking of AQA here, so it is worth 200 marks out of the 400 total).
It's of course a big step up from GCSE but IMHO with the new GCSE spec is not that wildly different.
@Moonlaserbearwolf the specs have changed massively since 25 years ago. I did French A level in the 1980s and we studied four books but wrote essays in English, much to DD's horror (she took French A level four years ago). Things do change.
@BeingGrownUp I'm well impressed with a class of 10 taking French! There were two in DD's class (which she does agree was a massive advantage esp in terms of speaking practice tbh).
I think either of her possible combos is good - both would leave an outlier (maths or history) but that's fine. Two sciences would pave the way to a science degree or even engineering; two arts would complement each other too.
If you can find out which board for A level French I can give more advice if helpful.