LDS scholars have a real answer here. Say so before your friend does.
1 Nephi 11:18 called Mary "the mother of God." 11:21 called Jesus "the Lamb of God, yea, even the Eternal Father." 13:40 said "the Lamb of God is the Eternal Father."
Joseph Smith inserted the words the Son of. Mary became the mother of the Son of God.
The Lamb became the Son of the Eternal Father. The change is small and it is not accidental.
FAIR says a translator may clarify his own work. Royal Skousen treats the change as clarifying, not correcting.
Both readings work, they say, since Christ is called Eternal Father in the book anyway.
Arguable. But watch the timing.
The edits land just as the teaching about God moves from one being to three separate ones.
"Why did those four verses need the words 'the Son of' added in 1837?"


Joseph was free to make his own work clearer, and Mosiah 16:15 still reads that way.
Three replies. FAIR says a translator may clarify his own work. Royal Skousen treats the change as clarifying rather than correcting. Christ is still called Eternal Father elsewhere in the book, at Mosiah 16:15. Other verses of that kind were left alone, which a systematic cover-up would not do.
Second, the phrase 'mother of God' drew Catholic-sounding objections from Alexander Campbell. Taking it out removed a stumbling block without changing doctrine.
Third, thousands of changes across the editions are simply typographical. These four are printed openly in Skousen's variant lists. Nothing was hidden.
Arguable, but watch the timing: the four edits land as his teaching about God moved.
Nobody disputes the facts. FAIR grants the four insertions and grants that Joseph Smith made them. Only the meaning is argued. The point that similar wording survives elsewhere is fair, and it does weaken a cover-up framing.
One thing is not explained well by any Latter-day Saint source. Why would a translation given by God need a fix about Christ? And why at exactly the verses a critic had attacked, in exactly the years his teaching about God was shifting?
As evidence of a text that changed with its author, this stands. As proof of wholesale rewriting, it overreaches.