If Keiko, who is brilliant even without the Skein and beyond even that when she uses the Skein, and who furthermore is a highly skilled ranged fighter with a large payout of explosives, and who furthermore has Hazo's trust and is therefore able to approach him without alarm, decides to kill him, he will be dead. "Attempt" is the wrong word here, is what I'm saying.
It's an "attempt" because Tenten (who came up with the idea of flowcharts all on her own, and thought it was a pretty clever idea) realises what happened and bursts into the Gouketsu living room, just as Keiko is screaming bloody murder at / pelting shuriken at her terrified and confused adopted brother, and manages to talk Kei down.