The Quran

فَلَمّا جاءَت قيلَ أَهٰكَذا عَرشُكِ ۖ قالَت كَأَنَّهُ هُوَ ۚ وَأوتينَا العِلمَ مِن قَبلِها وَكُنّا مُسلِمينَ

Muhammad Asad

And so, as soon as she arrived, she was asked: "Is thy throne like this?" She answered: "It is as though it were the same!"¹ [And Solomon said to his nobles: "She has arrived at the truth without any help from us,²] although it is we who have been given [divine] knowledge before her, and have [long ago] surrendered ourselves unto God!

Sc., "and yet not quite the same": thus, she expresses doubt - and doubt is the first step in all spiritual progress. She realizes that the "altered throne" is outwardly the same as that which she has left behind; but she perceives intuitively that it is imbued with a spiritual quality which the other did not possess, and which she cannot yet quite understand.
Thus Tabari, Zamakhshari and Ibn Kathir, on whose interpretation of this passage my rendering and the above interpolation are based.