I'm really stuck on the 20 minute thing as well.
Also, and again I'm not pointing any fingers at the parents, but it just seems odd that while they usually stay with her when they are in town, for this trip they didn't. The reason they gave was to not disrupt her since she had such early hours. But THEY are the ones that called her all the time (even when they weren't in town) to wake her up. So the not staying with her strikes me as odd.
I believe the dinner party they were at the night prior was also attended by her parents (or at least her mother, I still cannot figure out if dad was in town or not) And her mother stated how she ran after Anne as she was leaving to tell her she loved her. Again, I'm just devils advocate, but this just seemed kind of dramatic to me.
It just strikes me as such a coincidence that on this trip the parents weren't with her and she's killed.
Is Anne's bio dad still living?
I'm not even sure where my brain is with any of this, just questions that keep coming back to me.