1)
How did she know that he is Sha'ul?
1.
Rashi citing Vayikra Rabah 26:7: Normally the Mes ascends with his feet on top. Only for the honor of a king, he arises with his head on top.
2.
Radak (24): Really, she recognized him, just she feigned to discover this through the Chachmah of Ov.
