Does the Hadith "I and the guarantor of the orphan are like these two in Paradise," apply to one who marries a girl who is an orphan of both parents?

There is no orphanhood after puberty, and true orphanhood ceases with puberty. The Quran enjoins kindness to the woman who was an orphan, and whoever does so will be rewarded if they intend the countenance of Allah. The specific reward mentioned in the hadith is for whoever sponsors an orphan before puberty.