Each and every word of Asma bint Marwan told was correct. Did you notice the words that Muhammad attack his enemies by surprise. Even Asma's killing by Muhammad was done like this.
Asma had five sons when she was killed by Umayr ibn Adiy al-Khatmi by order of Muhammad. This was disturbing for B. Khatma tribe. Notice they converted to Islam after this incident because of the fear.
You can read about this in Kitab Al Tabaqat Al Kabir Ibn Sad, volume 2 page 30-31
And the Follower of Muhammad killed her while she was sleeping along her children in her house. He thrust the sword through her chest till it pierced upto her back.
For a Muslim to leave his religion, he only need to know about this prayer offered with Muhammad after killing a mother of five while she was sleeping in her house with her children.