I am NOT a lawyer.
Please talk to people who specialize in such delicate matters. Reddit is probably not the place for such complex guidance.
Some places where you might get better help or direction:
1. NCPCR (National Commission for Protection of Child Rights)
2. Women’s Police Station of your city
3. Bachpan Bachao Andolan bba.org.in
4.https://timesofindia.indiatimes.com/blogs/legally-speaking/corporal-punishment-against-children-and-the-law/
Please know that it is relatively hard to go against the child’s parents.
You might want to go through the above info & find a lady guidance counselor for her so she has a responsible adult to talk to… someone who is properly trained in child/ teen psychology.