I went to this official, accredited SDA web-site for this information, where SDA officials respond to more difficult questions about their founder, Mrs. Ellen G. White, that are not generally tackled in other official web-sites. https://whiteestate.org/legacy/issues-faq-unus-html/#unusual-section-d2 There was a question, “Jerusalem Never to be Rebuilt?” that seemed a potential source of information, and so it was. This is, indeed, directly related to whether she said Israel would never become a nation. She wrote in 1851 that
“old Jerusalem never would be built up.” 
The site responded to this by saying:
“…we find Mrs. White counseling the growing Adventist group that both
time-setting  and the "age-to-come" notion  were incompatible
with Biblical truth. She emphasized that the Old Testament prophecies
regarding the establishment of a Jewish kingdom in Palestine were
conditional on obedience and forfeited by disobedience. Unfulfilled
prophecies would be fulfilled to "true Israel" as unfolded in the New
Testament text. Thus the popular movement of the 1840s and 1850s to
promote a Zionist state in Palestine was not a fulfillment of Biblical
prophecy and not a quest in which Adventists should become involved.
Her warnings and instruction were designed to turn the interest away
from Palestine and toward the work God had opened up before them. In a
September 1850 vision she saw that it was a "great error" to believe
that "it is their duty to go to Old Jerusalem, and think they have a
work to do there before the Lord comes. . . ; for those who think that
they are yet to go to Jerusalem will have their minds there, and their
means will be withheld from the cause of present truth to get
themselves and others there."  Less than a year later, August 1851,
she wrote with greater emphasis "that Old Jerusalem never would be
built up; and that Satan was doing his utmost to lead the minds of the
children of the Lord into these things now, in the gathering time, to
keep them from throwing their whole interest into the present work of
the Lord, and to cause them to neglect the necessary preparation for
the day of the Lord." 
 Early Writings, p. 75. This sentence appears in the chapter, "The
Gathering Time," which combined two visions and some additional lines.
The first vision, Sept. 23, 1850, dealt with the "gathering time" of
"Israel," the dates on the Millerite 1843 chart, the "daily,"
timesetting, and the error of going to Old Jerusalem. The second
vision, June 21, 1851, focused on the third angel's message,
time-setting, and Old Jerusalem's not being built up.
 Many former Millerites were setting various dates for the return
of Jesus, with 1850 and 1851 being the latest dates for the end of the
2300-day/year prophecy. Although Sabbatarian Adventists generally were
immune from time-setting, Hiram Edson and Joseph Bates advocated 1850
and 1851, respectively. James White kept their views out of Present
Truth, the Advent Review, and the Review and Herald.
 With several variations, age-to-come exponents, led by Joseph
Marsh, O. R. L. Crosier, and George Storrs, believed that the Second
Advent would usher in the millennial kingdom on earth during which
time the world would be converted under the reign of Christ, with the
Jews playing a leading role. This group closely related to the
Literalists (British Adventists) who had believed that in the 1840s
the literal Jews would welcome their Messiah (Christ) in Palestine,
thus fulfilling Old Testament prophecies with Jerusalem becoming
Christ's capital during the millennium. The majority of the Millerites
had rejected this aspect of their Adventist theology, calling it
Judaism. (See Josiah Litch, "The Rise and Progress of Adventism," The
Advent Shield and Review, May 1844, p. 92, cited in Seventh-day
Adventist Bible Students' Source Book, p. 513. The first defectors
from early Seventh-day Adventists were H. S. Case and C. P. Russell
who had, among other concepts, embraced the "age-to-come" theory. See
The Seventh-day Adventist Encyclopedia, s.v. "Messenger Party."
 Early Writings, p. 75.  Early Writings, pp. 75, 76
(I have included the footnotes as they are important for a full understanding.)
From this it can be seen that SDA “Restorationist” doctrine accounts for the view that God was now dealing with ‘spiritual Israel’ (the Christian Church – themselves) and all the prophecies would be fulfilled in them, not literal Israel, which had forfeited its right to be established in the land. It appears that, due to these two visions of Mrs White, she discouraged SDAs from looking for a re-establishment of Israel because God was now dealing with them. Thus, “old Jerusalem never would be built up”, the SDAs claiming to be “new Jerusalem”. This equates with the idea that old Israel was not going to figure in God’s future plans for a nation like it had been before. The SDAs were the “new Israel” now.