Rights of Women in Islam

It is written in the book of jurisprudence in the chapter of marriage that it is not permissible to have intercourse with a woman before she is 9 years old. I understood from this that it is permissible to have intercourse with a girl starting 9 years old.
Through my work, I encountered many cases where girls would be subjected to extreme bodily harm because her body is not yet developed to handle sexual intercourse with the husband. Also in our societies and in our era today a girl in this age is still considered a child and does not yet have the mental and physical maturity to bear the responsibilities and duties of a contract with such importance. So why did God make permissible the marriage of a girl at such a young age? And is it true that a girl can be married off as soon as she is born?