Your acquaintance/ friend before becoming a Muslim would have conducted impartial research through which she reached the conclusion that Islam is the correct religion and this is exactly what she needs to do when it comes to the Shi'a Sunni discussion. The problem with debates is precisely this that it seeks to prove one path correct and the other side wrong and there is no scope for impartial research. History and what happened in regards to successorship after the Prophet has an impact on the belief system (re: Imamat) and the consequent laws based on the source from whom one derives their laws (Abu Bakr or Imam Ali).
As for the notion of 12 Imams, both Sunni and Shia schools of thought have narrated that there will be 12 Imams after the prophet, all who will be from Bani Hashim, and in some traditions, the names have been mentioned as well. If she is willing to do her research, I can compile a list of books to go through.
Brother of the prophet
Man and the Universe
The Lives of the Twelve: A Look at the Social and Political Lives of the Twelve Imams – available on Amazon. It is a series of books by Shaykh Pishvai and Amazon link is: