I've read a few of her books, and I quickly realized her problem. She's always trying to convey at least two messages: the one the book is about (in this case, the dangers of sex), and the other one which is prevalent in every book (except her last one, thank God).

The secondary message is: "It's not getting there, it's how you get there". And this often ruins the whole book. Because it will make her twist the entire plot just so at the end, we return to a similar state in the beginning. In this case, it changes from who's to blame for what happened.
Now, I don't have a problem with this message of 'the way is more important than the destination'. I (and I think most readers) have a problem with what she does to the plot and characters to get there (including character death in some books).

The last book of hers I read, Sing You Home, was actually somewhat worthwhile, because it gave a clear message without twisting the plot and story too much. I think her better books are for example, My Sister's Keeper, Nineteen Minutes and Vanishing Acts. They deal with more interesting issues, I believe, but there's also the advantage of not preaching about sex.

And just by the way: After writing Tenth Circle, she actually got to write some Wonder Woman comic issues.