I believe you did the right thing. I had a very similar situation last month. My husband has a partner in his business - the partner has a high school aged daughter that has babysat for us a few times before.
Long story short - we had her babysit, we got home earlier than she was expecting us - she had friends over (about 5 of them) and they were having a little "hot tub" party in our hot tub! She was all apologies etc. so so so sorry... yada yada - you get the picture. Anyways, as she's leaving she says, "don't worry - I'll tell my dad what happened."
After 3 days, we still hadn't heard anything from them so I called the partner's wife - we obviously know them well. All I had to say was, "Hi, did you hear about Saturday night?" And she said, with dread in her voice, "what did she do?"
Generally she is a good kid - and it could have been far worse - no alcohol or anything - my kids were safely tucked in and asleep in their beds etc. Just a bit of bad judgment - but I don't think we'll have her babysit again.
But I felt as a good parent, they needed to know what happened too.