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?