Is jealousy a real thing or what?

Hi everyone quick question. Do anyone else get like bad treatment from certain people? I have a co worker who been mad at me for something im assuming... an issue that took place between me and another co worker who is her friend. Apparently she stopped talk to me then about it. Even her friend stopped talk to me but we all good now except her. Almost a year and she doesn't speak with me but will continuously try to pick fights and have a problem with me. What is it that can be going on? Is she just mad or at this point is it jealousy?
Is jealousy a real thing or what?
Post Opinion