It has been suggested for many years that, women are each others worst enemies.
You do not necessarily have to be related to have 'issues'. The women at where I am doing my work placement are always slagging off co-workers behind their backs and then act all friendly to their faces.I avoid such office politics.
I don't think it is just jealousy, but can be an accumulation of a variety fo factors such as annoyance, insecurity and frankly having nothing better to do, that to cause friction!