Parent advice on babysitter etiquette

This is kind of long, bare with me, I'd love some advice or feedback.

My son is three and I've rarely needed a sitter but when I have, my best friends daughter (who's 15 now, 14 when she started sitting) has always been my first choice because not only does she have two little brothers my sons age and their family values are similar to my own, but my son knows and loves her. She's sat for us maybe a dozen times in the last year with no problems.

Last week though some things came up that I felt uncomfortable with (I actually posted about her using my computer). My concerns are that one of my sons toys was broken (according to him, she broke it, but he's three and has recently discovered the art of blame, and thus unreliable) and my son reported that she was using the computer while he was playing and while they were having dinner.

Now, the broken toy, no big deal, toys break, especially when boys are around. But I do think she should have mentioned it. As for the computer use, my rule (which I tell her every time she is here, and she has the same rule at her own home) is that she can use the computer after my son is in bed for the night (or nap), but not before. Really, all in all, not big issues.

So, I texted my friend and asked her to have her daughter call me this evening (she doesn't have her own cell phone or a home phone so this is my only means of communication) and she was really curious about why so I told her it was related to babysitting last week and no big deal. She kept questioning though so I told her the issues I had and what I intended to say to her daughter... something along the lines of, "I know you're babysitting for more and more families, thats great, Lachlan had fun with you but I wanted to remind you about my computer rule and ask you about the toy that broke. I'm not upset about the toy, it can be fixed, but it's nice to hear about these things because three year olds aren't always reliable!"

My friend was upset and offended that I planned to speak with her daughter before talking to her. My thinking was that they were very minor things and I've had a relationship with her daughter for 8 years, not to mention she is 15. My friend says I still should have come to her first and that's a standard, to keep the parents informed and let them make the decision if they should speak to her or I should. She then said that maybe her daughter shouldn't sit for us any more because it "felt awkward."

I don't have a teenager of my own and have only been a parent for 3 years, so I'm not going to pretend I know everything, I'm just going with my gut, here. But it seems like she's over reacting. Her daughter is 15, after all. When I was 15 and babysitting, I had clients call me directly, I don't think my parents were ever involved other than a friend asking them if I babysat and them giving out my number.

So... what's the norm here... has anyone had anything like this happen with a sitter and how did they handle it?