Why does it say "va'Titzpeno" (singular)?
Rashi #1: Sometimes a verse discusses a Rabim in the singular. Because she rushed to hide them in a small place, it is as if they were one.
Rashi #2 (citing Tanchuma): The spies were Pinchas and Kalev. Pinchas stood in front of them and they could not see him, for he was like an angel.
Rashi #3: She hid each by himself, therefore it is in the singular, like "Shemen u'Ketores Yismach Lev" (Mishlei 27:9)
Radak: This was so if the messengers will go to the roof, they will not recognize their place (amidst the flax; if both were together, it would be noticed).
If she hid the spies after the kings' messengers came, why didn't the messengers see them?
Radak: She already hid them before the messengers came 1 ; she sensed that the matter became known to the king.
Why did she say that she does not know where they were from, and to where they went?
Malbim: She wanted the messengers to leave quickly to chase them. To support that they are spies, she said that they asked about matters of the land, and concealed and did not say from where they are, and [when they left] to where they are.