Yes, there was some debate about this. Canonball thought yes because of her point cost, but with IMHO about the best overall magic in the game, decent CC, 4 actions, and all her other stuff, it jsut seems a bit much. I can read this either way, although the way the phrase "Whenever the Stygian Priestess enters CC, whether charging or being charged, she gets a free attack with the snakes writhing about on her shoulders.", seems to me to being the 1st CC action, not every model in a warband that attacks.
I acan see this going either way, just think that getting a fre first attack against any model that enters combat with her is a bit much. We ended up rolling d20 for this and canonball won, so we played it that she got 1 free attack whenever any model attacked her teh 1st action in CC. Priestess killed 2 Warhawks before they got her.