My advice is stay out of it.
There is nothing worse than someone else telling you how to parent when your kids aren't heading where you want them.
It's not all the mothers fault, girls are horrible! I was and I would be horrified to think that ppl though it was my mums fault I was doing stupid things... cos it wasn't, she had no control over me! (I must admit I wasn't THAT bad but I was out drinking and partying at 16)
Hope and pray that DSD pulls her head in and grows up. I did