Her inspiration is equal in quality to the inspiration of the Bible, but the function and purpose of Ellen White’s inspiration is different from that of the Bible. A parallel is found in Scripture. The prophet Nathan was as fully inspired as King David, but Nathan’s inspiration had a different function from David’s. David’s inspired writings became a part of the canon of Scripture. Nathan’s inspiration did not result in any canonical writings. TAWL 7.13
One cannot make differences in the quality of inspiration because inspiration is either present or absent, so that various manifestations of it cannot be distinguished by degrees. The Holy Spirit was just as careful in the superintendence of Nathan’s inspired messages as in David’s writings, although, in harmony with the divine purpose, only the latter were incorporated into the canon. TAWL 8.1
Ellen White’s writings do not function as a standard or rule for doctrine. The Bible does function in this manner. In this sense Ellen White does not have equal doctrinal authority with the Bible. TAWL 8.2