1)
Why did she say "now"?
1.
Malbim: Even after your death it would be a rebellion, since you promised kingship to Shlomo, and all the more so now, in your lifetime!
2)
Why did she repeat "now? you do not know"?
1.
Malbim: Even if he did not know about your Shevu'ah that Shlomo will succeed you, and he thought that you will consent that he inherit kingship, why did he hide this from you? How did you not know 1 ?
1
Malbim said (verse 17) that she did not blame David! We must say that he means 'how can it be that you do not know, i.e. he did not tell you?' (PF)
