There is an witness to the abduction, which you conveniently forget. Who saw a man and a woman in the car, and gave a description of the woman who abducted the child. 18 years later that child found in the company of Garrido, and the jury should be able compare the composite to the photo of Garrido's wife Nancy.
I presume the jury should be able to add two and two together.
I know there was a witness. But that was 18 years ago, and memories fade. It was also witnessed at distance and for a very brief moment. The witness has also been exposed to recent photographs of Nancy, which means that any testimony to the identity is tainted would be unreliable in isolation. The victim may have been found in their company 18 years later, but you would still need to make the connection between then and now. The defence could argue that the similarity is coincidental, and what would be your argument against that be? You would have none. The strongest way to make that connection is if Jaycee, Nancy or PG testifies to that fact. The other way would be if there was some physical evidence, tire tracks, parts of the car, parts of clothing, something like that which could be tied forensically to the Garridos, but as far as we know there is nothing like that. If I was a juror sitting on this case I would insist that that connection be made, since the means for making it is available. I would want to hear Jaycee, or Nancy, or PG say in court what happened that day. One of them. Anyone of them. If they did not I would feel obliged to aquit on that charge for lack of evidence, and I would not feel any remorse about doing that even though I think they are guilty, because all it would take to make that connection is for someone simply to talk.
That leaves the option of testimony. PG isnt going to testify against himself, particularly since there is nothing directly implicating him in the kidnaping other than what either Jaycee or Nancy might say. We would hope that Jaycee would testify, and her lawyer seems to think she will, but the NE article suggests that it may not be so certain after all. From the prosecutors point of view what do they do then to avoid the risk that she may not play? They could use hearsay from people she may have talked to in the interim (if that would be admissable when the victim is available to testify directly). The backup option is to turn one of the accused, with Nancy being the obvious candidate. She would certainly have motivation since she is the one most vulnerable. We have heard from various sources that she is cooperating with LE. Usually that means some sort of arrangement has been reached between the prosecutor and the defence, either in the form of reduced charges or a lighter sentence. Now, it may be possible that Nancy is unilaterally doing this in a hope for mercy from the judge in sentencing but I think that is less likely.
You need to stop being so emotional about this and look at it objectively. Consider how a case might be constructed in the most solid fashion possible. What could go wrong, what counter agruments could be offered up and how would those be addressed. Keep in mind that the onus is on the prosecutor to prove beyond reasonable doubt the facts of the case. Just saying it is so won't cut it.