This is a different story than it first appeared. At first, (at least to me) it appeared to be a normal high school boy driven over the edge by young love, and driven to commit the crime of passion for the girl he couldn't live without, in an instantaneous decision. That's not the case. He plotted this for awhile. This was not a case of exhaustion, and passion, and anger coming together in a horrible episode of spur-of-the-moment passion.
On the other hand, she needs to rethink how she behaves with boys. She needs to rethink how to behave in a way that she doesn't attract danger, and she needs to think about the kind of boys she will attract with her behaviors and photos and Karma.
Her parents seem like really, really lovely people. Besides calling the police to be there when they confronted this young couple when they returned home in the morning, it's hard to think of anything they could have done to prevent this.
Prayers for the other siblings in this family.