Not entirely correct since in the more full context she rejects "three gods" and states that the Holy Spirit is fully God and is not excluded --
Here is the chapter Bob. Please show us the full context for the statement that shows the Holy Spirit is fully God and not excluded. Because the statement lists one "being" that can enter the counsels and purposes of God.
It is impossible to explain the origin of sin so as to give a reason for its existence. Yet enough may be understood concerning both the origin and the final disposition of sin to make fully manifest the justice and benevolence of God in all His dealings with evil.
www.ellenwhite.info
Before the entrance of evil there was peace and joy throughout the universe. All was in perfect harmony with the Creator's will. Love for God was supreme, love for one another impartial. Christ the Word, the Only Begotten of God, was one with the eternal Father,—one in nature, in character, and in purpose,—
the only being in all the universe that could enter into all the counsels and purposes of God. By Christ the Father wrought in the creation of all heavenly beings. "By Him were all things created, that are in heaven, . . . whether they be thrones, or dominions, or principalities, or powers" (Colossians 1:16); and to Christ, equally with the Father, all heaven gave allegiance.
Ellen White says Christ is the only "being" in the universe that could enter into all the counsels and purposes of God. Even if she is using "being" in the sense of "person" in the traditional formula, she is missing a person in that statement. So how do you get from Christ being the only being that enters into the counsels and purposes of God, to there being Three in One? This statement ruled that out.
Now if by full context you mean some years later she started acknowledging the Holy Spirit as one of three "powers", or part of the "trio" or the three "dignitaries", etc. and indicated the Holy Spirit has a personality, and that the Holy Spirit is part of the Godhead, then yes, that is true. But those later statements cannot match up with statements like the above, which are not compatible with Trinitarianism.
In her early statements, while she mentioned the Holy Spirit, for instance, descending at Jesus' baptism, etc. she did not attribute to the Spirit a peronality, etc., or indicate that the Holy Spirit was part of the God head.
But it is not just a matter of not mentioning it. If Jesus is the only "being" that can enter into the counsels and purposes of God, then
a. the term "being" is used in a meaning similar to "person" in the traditional formula, but you only have two persons
b. The term "being" is used in a different way, and "God" and "Christ" are two separate beings.
See how much of a difference it makes when one who actually believes SDA doctrine gives the view that SDAs have of a given topic.
I think that is very "instructive" for the unbiased objective reader that honestly want to know what SDAs believe rather than how this-or-that could be spun in a direction that almost no SDAs accept.
Numerical acceptance of one view or the other is not what was highlighted. There were a number of non-Trinitiarian SDA's in early SDA history. There are still some today. And there were even some posting on this forum for a time, but I don't think they are here any longer. And there are still anti-Trinitarian Adventists who publicize their views online.
The larger issue is that Ellen White's statements changed over time. And while I would say relatively few SDA's now reject the Trinity, many SDA claim to accept the inspiration of Ellen White. But the statement of Ellen White from the Great Controversy is not describing the Trinity they claim to also accept.
It is arguable that her later statements represent a similar conception to the Trinity, but in different terms, due to some disagreements with the language of Trinitarian creeds. Even then various Adventists have noted that her unity arguments framed around relational unity leave room for tritheistic understandings.
If you were to argue that Ellen White paved the way for Trinitarian thought being largely accepted in the Adventist church, I would agree with you completely. I would argue that some of her later statements sound very Trinitarian. Starting in 1890 she seemed to make progressively more Trinitiarian arguments, and clarified elements regarding the Son and the Holy Spirit.
But that doesn't change that her early writings, which the church claims inspiration for, did not match up with the Trinity.
EDIT:
I wanted to clarify one point. If by "not entirely" you mean that her later statements could be taken as fully Trinitarian, and not tritheistic, in that we agree. I think some of her statements certainly could. Other of her statements sound ill advised if you wanted to not convey tritheism. But her further clarifications regarding the Son and the Holy Spirit, and the use of the formula in the great commission regarding the singular name of the Father Son and Holy Spirit do for me indicate that she in later years held a view of Three in One that she never put in those terms due to the history of those terms in the movement.
But that doesn't change her earlier statements, which are not compatible with Trinitarianism.