Personally, I would feel beyond uncomfortable talking to "these parents" directly if it was my daughter who got lined up and yelled at. Especially the dad. I'd be practically terrified. Nope. Wouldn't do it unless I was able to ensure that I was speaking with the mother alone.
The whole CPS thing was never even brought up by the OP, so I'm not sure why it is pertinent to this thread, except that perhaps the counselor might be required to report something.
It's really not this fear scary thing - it's very simple, "hey, my dd said this happened, what did the girls do?" if you can't talk to these people how could you let your child sleep at their home?
It almost begs the question what is wrong with a person that lets their child sleep at another's home but can't ask what happened?!
and it's really that BAD and you are this terrified- it's a police matter, not a third party (school counselor)
ETA- really that terrified of asking a simple "what happened?" I would say you are not looking at this in proper perspective.
Certainly if I knew about this before hand, I would never allow it. I'm not sure how it would have been inferred in my post--knowing beforehand and letting her go anyway. And, OK, I would not be terrified for my life or limb or anything requiring police interference, but socially afraid of approaching the father. So, fine, remove terrified--a poor word choice considering the subject of the thread making it possible to confuse physically and socially terrified. I would still dread bringing this up-- and not just in a way that I dread an unpleasant phone call, but dread that I might be caught up in a fight (verbal, to be specific) with someone who has been strangely controlling and yelling at my daughter. So much so that I might prefer the third party approach if I felt like something needed to be brought up to someone. If not, I would simply drop it.
I'm not saying I would take the same approach as the OP, but I don't think it was wrong.