Hi,

It will be better to start the preparation as soon as possible. She can start preparing from class 11.

Infact the whole syllabus from class 5 to class 12 is basic for preparing the IAS exam. Subject like maths, science, history geography economy etc. Provide  the basic information. If she focuse on the curriculum with sincerety her school preparation also help her in the competitive exams preparation.

Hope this helps.