How can wife apply for divorce under Muslim Law

One of my friends (Muslim Female) married around 10 years back at the age of 18-19 years. From day one her husband put lots of restrictions on her from talking,eating,dressing to even small small things. She was literally not allowed to visit any of her relatives (Except Parents).He always raised doubts on her modesty and was hurling lots of abuses.Her life was more like hell and virtual prison due to mental harassment (No physical harassment except some small instances but aggression was always there).During these times they had two kids.But things were worsening day by day.But finally after 3-4 years, she took admission in MBBS and stopped to meet her husband but he used to call always abuses and raises baseless allegation of relationships with multiple doctors.During her education not a single penny was paid by her husband.Now her education is over and wants divorce as he has still not changed.She wants to re-marry after handing over the kids to him. Pl sgst hw 2 apply Khula?