Pillar of Fire, Pillar of Truth is super! Also, anything by Patrick Madrid is good. He has many books dealing with Catholic apologetics and conversion. Such as his Surprised by Truth series. Each chapter in these books are a conversion story of a different person to the Catholic Church and their reasons for becoming Catholic. Book 2 has a conversion story of a former Mormon, Steve Clifford. His chapter is titled, “From the Latter Day Saints to the Communion of Saints”.
Other good books are:
Where is That in the Bible, by Patrick Madrid
Why is That in Tradition, by Patrick Madrid
The Gift of the Church, by Monsignor Bob Guste
Why Do Catholics Do That, by Kevin Orlin Johnson, Ph.D
The Scriptural Roots of Catholic Teaching, How the Bible Proves the Truth of the Catholic Faith, by Chantal Epie
Eucharist, God Among Us, by Joan Carter McHugh
A Concise History of the Catholic Church, by Thomas Bokenkotter
There are also wonderful booklets on the Catholic faith and history put out by the Knights of Columbus called, "The Luke E. Hart Series, Basic Elements of the Catholic Faith.
God bless you for your efforts in trying to bring your Mormon friend God’s truth. My prayers are with you.
Jesus doesn’t expect us to be successful, he expects us to be faithful. - Mother Theresa -