Kate's theory seems pretty sound to me, although I was thinking along opposite lines.

The advancements in tracking down suspects using familial DNA (as in the arrest of the Golden State Killer) mean that it's now possible to identify unknown victims as well. The first step in finding justice for this little girl is going to be finding out her name. Once that is ascertained, her parents can be interviewed/interrogated. With a child this young, the parents would always be the first suspects--even more so when the child has a life-long condition that would require life-long care.