LDS scholars have a real answer here. Say so before your friend does.
It is strictly monotheistic, and the Father-Son unity is so tight it reads almost as one person in two roles. Mosiah 15:1-5 has Christ as "the Father and the Son… one God." Alma 11:26-29 says there is one God and no other.
That the Father, Son and Holy Ghost are three separate beings. That the Father has a body of flesh and bone.
And that faithful people may become gods themselves.
David Paulsen of BYU says the 1830 text read whole is not modalist. It does tell Father and Son apart in other places.
He adds that early Christian writers were loose with words too, before the councils tightened them.
Arguable on any one verse. Harder to argue with is the direction of travel.
The 1830 book sounds much more like ordinary Christianity than 1844 does.
"Read me Alma 11:26-29 in your own book. How many Gods does it say there are?"


Read whole, the 1830 text does tell Father and Son apart, as the New Testament does.
David Paulsen and Ari Bruening of BYU argue the 1830 text is not modalist when read whole. It does tell Father and Son apart. The Father's voice introduces the Son in 3 Nephi 11, and Christ prays to the Father.
So its 'one God' language describes a unity of distinct persons. That is no further from later teaching than the New Testament's own 'one God' texts are from Nicaea.
Mosiah 15 is explained by divine investiture. Christ acts as Father by creation and covenant, and as Son in the flesh. The First Presidency set that out in 1916. Brant Gardner adds that the modalist ring may come from the limits of translation language.
Arguable on that one charge, but the 1830 book says nothing of the later teaching.
The narrow charge of modalism is genuinely arguable. Critics do sometimes overstate it. Paulsen really does find Father and Son told apart in the text.
The broader point survives anyway. The Book of Mormon insists on one eternal God. It says nothing at all about many gods, about eternal progression, about God having a body, or about people becoming gods. Those doctrines define mature Mormonism, and the 1830 book is silent on every one.
The 1916 divine-investiture framing exists because the plain text does not teach the later doctrine.