Is possible for a married coworker to get jealous even though she would never cheat?

I have a female coworker. We text and joke around all the time. But she is married so I know where the line is and know not to cross it. She is clear she would never cheat on her husband she loves. But she still gets jealous when I talk to other female coworkers. Why? If she would never do anything anyways.
Is possible for a married coworker to get jealous even though she would never cheat?
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