Because she was planning to kill him. If you watch the episode when Michael Jr. kills Snoop,he is shown watching the location where he is scheduled to meet with Snoop several hours before it occurs. He sees Snoop letting several men (probably Marlo gunmen) into the building before their meeting.

Who did Marlo shoot devonne?

Marlo and Partlow later tracked Devonne to her home and Marlo murdered her personally as she was leaving one night. The violence continued to escalate and Marlo's lieutenant LaTroy was killed. When Stringer Bell was murdered, the police and drug gangs thought it was Marlo who had him killed.

Who killed Stringer Bell?

Stringer at first tries desperately bargaining for his life, but when Omar reveals that he and Mouzone are after him for personal reasons, and that Avon has betrayed him, he sombrely resigns to his fate and is shot to death by Omar and Mouzone.