i'd be willing to bet that your coworkers are not actually afraid of this person. there comes an often distinctive time in your employment that you realize the people in charge are aware of certain antics and choose to not do anything about them. it may be that she's shift coverage or flies under the radar, etc. your coworkers likely have chosen to not pick this fight because they don't think they'll be supported by anyone that has power to do anything as well as they don't want to be targeted regardless of HR policy. i hate to say it but i think you should just let it go. you could talk to the lab manager, but they'll likely just speak to your supervisor whom is going to speak to her at that point. what is going to come of that? my guess is she'll deny everything and has no concrete proof against her beyond he said she said, so it'll get pushed under the rug and things will be business as usual. it may turn out differently though. this is just my educated guess after seeing this type of coworker various times in my career.