What are the two ways you might solve this conflict?

Have a meeting and make a general statement on how negative behavior in the workplace is not tolerated and how it will cause negative or adverse actions on our project.

I would have a meeting and start it off by explaining the rules of engagement and how negative behavior will hinder our ability to work as a team. Iwould also privately engage the member involved in negative behavior and explain to her how her behavior is counter productive and it may affect our bottom line goal.