1)
Did she not see David until she was close enough to prostrate in front of him?
1.
Radak (20): Due to the mountain, they did not see each other until they met. She descended on the hidden part of the mountain.
2.
Malbim: Through hearing David's words, she recognized and saw him. Kli Yakar - it was night, so she did not know that it was him until she heard his words.