I agree with you.
The DA I'm sure is reluctant to take on a case this weak. I mean, we're all pretty sure what went down and that she was involved to some degree, but proving that to a jury beyond a reasonable doubt when the kid is wailing and crying on the stand and the bad guy is insisting she had nothing to do with it would be tough.
It would also jeopardize their prosecution of the main offender.
I don't know how they do things in those parts, but my money's on her having made a deal to testify in exchange for non-prosecution of what amounts to a fairly weak case. If so, this will come out when Ludwig's lawyer files a "Reveal the Deal" motion.