“God has given me light regarding our periodicals. What is it? -- He has said that the dead are to speak. How? -- Their works shall follow them. We are to repeat the words of the pioneers in our work, who knew what it cost to search for the truth as for hidden treasure, and who labored to lay the foundation of our work. They moved forward step by step under the influence of the Spirit of God. One by one these pioneers are passing away. The word given me is, Let that which these men have written in the past be reproduced.” — (Ellen G. White, Review and Herald, May 25, 1905, 'The work for this time', address at the 1905 General Conference, May 16)
Not only did Ellen White not rebuke the pioneers for their anti-Trinitarian writings, but God instructed her to make sure that the writings of the pioneers were reproduced. So from this alone we have two choices. Either she was a false prophet and had no trouble with others teaching serious error on something as important as who the Father and Son are. Or the non-Trinitarian view is correct.
We should expect no less since the non-Trinitarian view was a God given Pillar of faith.
“Those who seek to remove the old landmarks are not holding fast; they are not remembering how they have received and heard. Those who try to bring in theories that would remove the pillars of our faith concerning the sanctuary or concerning the personality of God or of Christ, are working as blind men. They are seeking to bring in uncertainties and to set the people of God adrift without an anchor.” — (Ellen G. White, MR760 9.5, 1905)
“Here we might mention the Trinity, which does away [with] the personality of God, and of his Son Jesus Christ,” — (James White, Review and Herald, December 11, 1855, p. 85)