In the UK, up to the age of 14 (Year 9), children study a broad range of subjects that includes (in almost all state schools) English, maths, science, history, geography, PE, ICT, design and technology (often includes art, food technology, design, and textiles) a modern foreign language (often French or German).
At the age of 14 (end of Year 9), the pupils choose 7, 8 or 9 of these subjects (and other subjects like media studies, photography and separate science might also become available as choices) that they are particularly interested in, and choose to study these for 2 years (through Years 10 and 11) as GCSE's. Most GCSE courses have an exam at the end of Year 11, though some are 'modular' and have exams and/or coursework all the way through. Every pupils has to study English, maths and science - some schools also insist on ICT, but after that the child can usually choose their own subjects.
At the age of 16, pupils who plan to stay on at school (if it has a 6th form) or who are going on to 6th form college can choose their A-Levels.These come in 2 parts - the first year is called A/S levels and in Year 12, usually pupils choose 3 or4 A/s -Levels. At the end of Year 12, exam results often mean that pupils will drop one A/S level and just take their 'best' subjects for A-Level. During Year 13 (last year of 6th form / college), pupils make applications to colleges and universities for degree courses.
A/S and A-levels, and GCSE's are not the only way to go, though they are a common route. There are also Diplomas, which begin in Year 9 and offer a more vocational route, often incorporating a qualification called a BTec, which is the equivalent to 2, 3 or 4 GCSEs. You will need to talk to your dd's tutors and to her about what is best for her.
It's also really important for her to get some good careers advice leading up to her choices in Year 9 and Year 11 so she is sure she can get into the course she wants after she leaves school. There are some really good websites and the school will have a careers advisor too.
Hope that helps!