Yep, the third Eve Duncan book I read was the conclusion of the great mystery of Bonnie's disappearance, and I'm definitely glad that I read it sooner rather than later. I didn't have to read through 13 books (dear God) first, the final chapter dragged into a tedious trilogy (although I did eventually read "Eve," too).
"Bonnie" is one of Johansen's books, including those I've read from the Eve Duncan series. In fact, it and "Blood Game" are probably my favorites.
That said, even "Bonnie" had a lot of weaknesses. First of all, the "Eve"/"Quinn"/"Bonnie" trilogy was a blatant marketing ploy, and a dirty trick in my opinion. It's one thing to do a cliffhanger to leave your readers wanting more. It's another to make them trudge through an entire two books, knowing that neither one of them is going to solve the mystery.
Note: The following paragraph contains a small spoiler.
In "Blood Game," we discover that Joe can now see ghosts, including Bonnie. In this book, someone else gets to see Bonnie, too. It's getting kind of ridiculous, and it makes Eve's relationship with Bonnie seem less "special." Bonnie's role grows in this book, and she's even seen comforting a deer as it dies. A deer? Why would a deer have a human comforting it? Shouldn't it have another deer? Aren't there deer ghosts/angels? The whole scene was pretty corny, and it made Bonnie seem even less human than she did before. No child is that perfect, people.
End spoiler.
There's also a character with a disability in this book, and while it's always good to have representation, he's portrayed as what TV Tropes calls "Inspirationally Disadvantaged" (Type C, if you're curious). I'm not at all surprised that Johansen made him "special" (and I don't mean that as a euphemism for "developmental disability." It's more like, he's special because his disability allows him to see/sense things others can't.). I'm sure she thought that this sort of portrayal is progressive. But people with disabilities don't exist for able-bodied people. We deserve to be portrayed as more than just "special." We deserve to be well-rounded, to have strengths and weaknesses and emotions of our own.
In addition, there's yet another "false flag" operation portrayed by an "Arab" government, in one of Ted Danner's flashbacks. There were so many opportunities for Johansen to show that the American government could be just as corrupt, but no, the Big Bads are always Middle Eastern or European. (Almost always--one was Australian.) But at least with Europeans, they're individuals. With Middle Eastern situations, it's implied to be very powerful governmental groups. It's just another example of American exceptionalism in fiction, and it adds to a culture that's already overly xenophobic.
As for the solution to the mystery of Bonnie's disappearance, I know that not everyone's going to accept it. I personally liked it for the sole reason that I didn't expect it. In retrospect, it made sense, and I'm sure plenty of readers guessed it. But it doesn't matter.
Unfortunately, it seems Johansen is still churning out more Eve Duncan books. Bonnie's killer has been found. Don't put Eve through more crap than she's already had to deal with. For God's sake, let the poor woman move on with her life.