According to the official rulebook, most politically minded Sigmarites of the Empire consider the Sisters to be unworthy. while the witch hunters consider them to be heretics. The Sisters possess an item called The Script of Sigmar in their convent, The Rock, and the witch hunters desperately wish to claim it. The Sisters were exterminating any survivors of the comet blast believing themselves to be the only Sigmar worthy survivors. I’m assuming your question has to do with possible alliances so between Sisters and Old Lady Burners I would say no, but then again anything can happen with the right story line.