Glad that you are encouraging your sister to become a cricketer at this young age.
1. She can join a good cricket coaching academy for weekend sessions, daily sessions based on the affordability and accessibility. She needs attention to her nutrition and exercise regimen to develop her stamina and fitness levels.
2.If available, choose a club that has facilities for training girls. For instance, Karnataka Institue of Cricket in Bangalore has an exclusive women's cricket coaching and the entry age is from 6 years onwards. (http://www.kioc.net/)
3.You can also consider summer camps that are held in most cities and cricket clubs for 2-3 weeks.
4. If you find a club or academy that focusses on children, it would be ideal. Try something similar to this Academy started by Virender Shewag. It has a Junior pitch program, wherein children less than 14 years are given an insight into competitive cricket focussing on fitness, team spirit, fundamentals etc.(http://sehwagacademy.com/junior-pitch).
5. Many of the IPL teams also have a commitment to nurturing young talent. For instance, Delhi Daredevils have a 3-month coaching camp for children from 6 years and above (http://www.delhidaredevils.com/5291-2/). You can look at this option based on the city you live in.
6. Once she has settled down then from the academies you can develop contacts with coaches and talent scouts who can get her ready for a under 16 or other junior tournaments.
7. Last but not least, you need to keep her regular education and subject tuitions in mind and judiciously use the available time so that studies get prominence.