Good concrete advice from dlh! Like the non-confrontational approach since you 'll continue to work together. Another thought is to go at it from a process angle: like say you have an idea on how to manage/keep track of all the projects you have going on so you can all be on the same page... you could suggest using something like google documents or PTO Manager to better manage your projects. Maybe by putting some type of system in place will reign her in a bit?
Also, here are some articles that you might find helpful:
How To Deal With Difficult People - PTOToday.com
Lisa
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