What is the root of "v'Nachbesem"?
Radak #1: It is Nichba (hiding); the Aleph is missing.
Radak #2: The root is Chavah, with a Hei. We find this root with a Hei.
How did she know that the pursuers will return after three days?
Rashi: She knew through Ru'ach ha'Kodesh. 1
Radak: She reasoned so, for it is one day's journey or a little more until the Yarden. Three days suffices to reach the Yarden, search 2 and return.
Radak brings so from Chazal. Yefe To'ar (on Bereishis Rabah 56:1) did not know the source, if not that Hashem does not leave Tzadikim in distress for more than three days (Bereishis Rabah 91:17).
Why would they search after the first day? If they fled to return, surely they ran as fast as they can, and reached it in less than a day (the time for one who walks normally), and crossed immediately! Perhaps they heard that one of them looked very old (Kalev was 85); they did not know that he was still strong (14:11) [and could go quickly
Why did she say "l'Darkechem"?
Malbim: You will be able to go on the straight path. You will not need to take a crooked path,