According to Malcolm, it took Ella five years to convert to Islam (Chapter 13).
Ella started going to hear Malcolm preach the message of Islam in the little mosque he was able to open. Malcolm had "never even thought about converting her", as he knew how "toughminded and cautious about joining anything" she was. He notes with half-way serious humor that "(he) wouldn't have expected anyone short of Allah Himself to have been able to convert Ella" (Chapter 13).
When Ella expressed her desire to "follow the Honorable Elijah Muhammad" five years later, Malcolm, understanding that "those who (were) the hardest to convince (made) the best Muslims", knew his sister would be a great asset to the religion (Chapter 13). He was not disappointed - with characteristic zeal Ella began to study under Boston orthodox Muslims, founded a school where Arabic was taught, and financed Malcolm on a pilgrimage to Mecca (Chapter 17).