What did Ellen White believe regarding the Godhead?

Ellen White never used the term "trinity," although she did refer to the "three living persons of the heavenly trio" (Evangelism, p. 615). She believed in the full deity of Christ, stating that "Christ was God essentially, and in the highest sense. He was with God from all eternity, God over all, blessed forevermore" (Review and Herald, April 5, 1906). She also referred to the Holy Spirit as "the Third Person of the Godhead" (The Desire of Ages, p. 671). Her comments, as collected in Evangelism, pages 613-617, suggest that she believed that the Scriptures taught the existence of three co-eternal divine persons.

Did Ellen White believe the Holy Spirit is a divine person?

Yes, but at times she used the pronoun "it" when referring to the Holy Spirit. Several statements regarding the personality of the Holy Spirit are collected in Evangelism, pages 616, 617. In 1906, for example, she wrote, "The Holy Spirit has a personality, else He could not bear witness to our spirits and with our spirits that we are the children of God. He must also be a divine person, else He could not search out the secrets which lie hidden in the mind of God. 'For what man knoweth the things of a man, save the spirit of man which is in him? even so the things of God knoweth no man, but the Spirit of God'" [1 Corinthians 2:11] (Evangelism, p. 617). (To view Ellen White's original, unedited draft of this passage, click here.) See also the PDF document: "Ellen White's Trinitarian Statements: What Did She Actually Write?