Albert Barnes Commentary 1 Samuel 19:17

"And Saul said unto Michal, Why hast thou deceived me thus, and let mine enemy go, so that he is escaped? And Michal answered Saul, He said unto me, Let me go; why should I kill thee?" — 1 Samuel 19:17 (ASV)

Why should I kill you? - To avert Saul’s anger from herself, she pretended that David had threatened her life unless she facilitated his escape.