Many have wrongly concluded that Ellen White taught the Holy Spirit was another being because she called the Holy Spirit a person. But she was in fact referring to the Omnipresent Spirit of Christ who she called a person, not another being.
“When trials overshadow the soul, remember the words of CHRIST, remember that HE is an unseen presence in the PERSON of the Holy Spirit, and He will be the peace and comfort given you, manifesting to you that He is with you” — Letter 124, March 7, 1897; Daughters of God, p. 185.2, 1897
“Lift up CHRIST in His power in the PERSON of the Holy Spirit. He is waiting for them to open the door and admit Him.” — Letter 59, March 29, 1899
“CHRIST has left HIS Holy Spirit to be HIS representative in the world, to give celestial aid to every hungering, thirsting soul.” — Letter 84, October 22, 1895
Ellen White above states that the Holy Spirit is the Spirit of Christ and that His own Spirit represents Himself in the world. Therefore, the next quote is also saying that the Holy Spirit is the Spirit of Jesus Christ which she calls a person.
“JESUS is present in the PERSON of His representative, the Holy Spirit, reviving the hearts of the humble and contrite ones.” — Manuscript Releases 12, p. 145.2, 1898
“The HOLY SPIRIT is the SPIRIT of CHRIST, which is sent to all men to give them sufficiency, that through His grace we might be complete in Him.” — Manuscript Releases 14, p. 84
“The HOLY SPIRIT is the SPIRIT of CHRIST; it is His representative. Here is the divine agency that carries conviction to hearts. When the power of His Spirit is revealed through the servants of God, we behold divinity flashing through humanity.” — MR13, p. 313.3, 1895
“We want the HOLY SPIRIT, which is JESUS CHRIST. If we commune with God, we shall have strength and grace and efficiency.” — Letter 66, April 10, 1894
“God help us that we may be sanctified through the truth and that sanctification shall have its influence to leaven those that are around us—not the leaven of malice, not the leaven of jealousy, not the leaven of evil surmisings, but it is the leaven of the SPIRIT of JESUS CHRIST, which is sent down from heaven, called the HOLY GHOST, and that Spirit affects the heart and the character.” — Manuscript 36, 1891
“CHRIST has left HIS HOLY SPIRIT to be HIS representative in the world, to give celestial aid to every hungering, thirsting soul.” — Letter 84, October 22, 1895
“CHRIST came to our world, but the world could not endure His purity. He has gone to His Father, but HE has sent HIS HOLY SPIRIT to represent HIM in the world till he shall come again.” — Manuscript 1, January 11, 1897