Do parents hold their children accountable for their bad behavior

or do they just continually blame everyone else's child instead?  I have a 15yo was sleeping over at a friend's house with two other girls.  They were at the grandma's house and the grandma let them pitch a tent out in the back yard (she lives in the country) and "camp out."  Problem is sometime in the middle night while the grandparents were asleep, after testing back and forth with an older boy (18 years old), he shows up picks all four girls up and takes them to one of the other girls' house whose parents were not home.  Long story short, there was marijuana involved and a picture was taken one of the girls (not my daughter) smoking it.  Of course the picture found its way to Snapchat or some other social media and the girl's (the one in the photograph) parents saw the picture. 

My daughter, knowing that their secret was out and that it was only a matter of time until I was made aware, tearfully confessed all to me.  My daughter is normally a rule follower to the T.  Makes straight A's and lives for her the praise she receives from me, her teachers, and her friends' parents.  So she was sick at what she had done.  I asked her if she had smoked and she said no.  That she was there, but she didn't smoke it.  I made her take a UDS and she was clean.  I then grounded her from her phone, from any social interaction.  She can go nowhere and she can do nothing but chores, homework, etc. until I've decided to trust her again.  I found out who the older boy was and I have told him and his parents that he had better stay away from daughter - no texting, no calling, NOTHING or I will call the police.  I spoke with two of the other girls' mom's who have grounded their daughters.  We are all on the same page except for the one girl's mom and stepdad.  These parents have grounded their daughter, but have proceeded to blame everyone else involved in it.  They have called the grandparents whose house the girls were at originally and basically screamed at them.  They have texted them endlessly and sent them the picture of their daughter smoking repeatedly.  I spoke with the grandparents and told them they should block these people's number which they did.  The parents have called me and the other mom's telling us their daughter is not going to be allowed ours and that they are going up to the school to make sure their daughter has no classes with ours at all.  They said our daughters peer pressured their daughter into doing what she did and that basically their daughter would never do anything like this if hadn't been for my daughter and the others.

Here's the thing, I'm fine with our daughters not being friends anymore.  I think that it might not be a bad idea.  There are some issues with this girl that go deep.  My daughter has told me how the girl sneeks makeup and different outfits to school and changes at school.  The girl has lied to her parents about where she's going so she can hang out with a boy.  Stuff like that.  So I'm thinking they shouldn't hang out together anymore.  My problem is I didn't blame anyone for my daughter's bad decision.  She made a bad decision that night.  She knew it was wrong to get into a car with that boy.  She knew it was wrong to go to the other girls house without telling anyone and without there being a parent there.  She most definitely knew that they should not be anywhere near marijuana.  So when I punished her she knew that it was because she made a bad choice, a wrong choice.  And I would not even hear anything else about whose idea it was to do what.  It didn't matter.  They ALL participated.  So for this one girl's parents blaming everyone else rather than making their daughter take responsibility for her own actions just angers me.  This girl is learning that in the future when she lies or gets caught in trouble again, she can just blame whatever friend she is with and her parents will buy it hook, line and sinker.  That right there is why my daughter won't being hanging out with her anymore.  These people are clueless!

Finally, I received one last text from the mom who basically said wouldn't people be shocked to find out that my "good little straight A girl" was partying.  So I reminded her that it was her daughter photographed hitting a bong and she should be very careful about throwing stones at glass houses.  I haven't heard from her since.

I just don't understand this blame everyone else mentality.  Just take some responsbility as a parent and make your children take some responsibility for their actions.  I'm truly upset by what my daughter did.  I feel like I somehow failed.  I gave her too much freedom, too much trust and she was too young, she wasn't ready.  But I'm not responsible for everyone elses kid nor is my daughter reponsible for her friends!