1)
What is the meaning of "Ko Ya'asun Elokim"?
1.
Rashi: Like you did to Nevi'ei ha'Ba'al.
2.
Radak: This is like a Shevu'ah, like "Ko Ya'aseh Li Elokim v'Cho Yosif" (2:23). She used the plural (Ya'asun), for she intended for the gods she serves - Ba'al and the Asherah 1 .
1
Radak: A mistaken text of Targum Yonasan says 'the fear of Hashem.' The correct text is like I explained.
2)
Why didn't she [try to] kill Eliyahu immediately?
1.
Malbim: She saw that Achav leaned [to serve Hashem] after Eliyahu and justifies him; she was not brazen to kill him immediately. She thought that at night, Achav's heart will return to his evil.