In great mercy, according to His divine character, God bore long with Lucifer. The spirit of discontent and disaffection had never before been known in heaven. It was a new element, strange, mysterious, unaccountable. Lucifer himself had not at first been acquainted with the real nature of his feelings; for a time he had feared to express the workings and imaginings of his mind; yet he did not dismiss them. He did not see whither he was drifting. But such efforts as infinite love and wisdom only could devise, were made to convince him of his error. His disaffection was proved to be without cause, and he was made to see what would be the result of persisting in revolt. Lucifer was convinced that he was in the wrong. He saw that “the Lord is righteous in all His ways, and holy in all His works” ( Psalm 145:17 ); that the divine statutes are just, and that he ought to acknowledge them as such before all heaven. Had he done this, he might have saved himself and many angels. He had not at t…
"The Lord is righteous in all his ways, and holy in all his works."
Ellen White directly references Psalms 145:17 in this passage.
"A compassionate Creator, in yearning pity for Lucifer and his followers, was seeking to draw them back from the abyss of ruin into which they were about to plunge. But His mercy was misinterpreted. Lucifer pointed to the long-suffering of God as an evidence of his own superiority, an indication that the King of the universe would yet accede to his terms. If the angels would stand firmly with him, he declared, they could yet gain all that they desired. He persistently defended his own course, and fully committed himself to the great controversy against his Maker. Thus it was that Lucifer, “the light bearer,” the sharer of God's glory, the attendant of His throne, by transgression became Satan, “the adversary” of God and holy beings and the destroyer of those whom Heaven had committed to his guidance and guardianship. PP 39.2"
"The Lord is not slack concerning his promise, as some men count slackness; but is longsuffering to us-ward, not willing that any should perish, but that all should come to repentance."
Both passages discuss God's longsuffering and desire for repentance, even towards those who have rebelled. The EGW passage applies this to Lucifer, while 2 Peter 3:9 applies it to humanity. The connection is thematic, focusing on God's character of longsuffering.