SO TRUE. Joined a lab sophomore year with all women (except 1 guy). I thought everything was going fine (and confirmed with the RA many times), until the end of the semester, when one of the other girls there told me that all the other girls in the lab were **** talking me and that the the RA would "recommend" a "bad" grade to the PI for me. Now, I knew that I would have issues with the RA the moment we met. RA didn't like how PI had allowed me to "join the lab so quickly" and how PI made RA in charge of me, which meant more time "wasted" to "pointlessly" train me). Anyways, the girl (the only angel there) informed me that she was also disgusted at RA's behavior and the lab's endless gossip: all the other women in the lab crap talked the PI 24/7 every time she left the room. Then they would crap talk each other when one of them left the room. In the end, I learned then and there to demand a syllabus or some sort of "coursework" guideline so I don't get screwed over again by ambiguous/subjective grading. Tears were shed, and I actually ended up arguing with the PI at how unfair and how misleading RA was and PI ended up agreeing... 1 month later. BTW, as for the 1 guy in the lab, RA adored him and always gave him free passes. He skipped lab many times, wouldn't stop talking/gossip, and she'd always cover his ass and give him a "glowing" report. Ugh.
So yes, imo, women are more vicious to each other (I've heard other stories as well). Overall, horrible lab experience and never looked back.