Hard to swallow.
If you ever study child development (like in a University) you soon learn that there are specific times and sequences that have to happen well, basically in the correct order and at the proper time.
Language development is one of them. Google Piaget.
AFAIK, all the other verified examples of feral children, none of them ever attained anything approaching even average language skills.
she was kidnapped when she was five
before being abandoned in the jungle.
The typical 4-year-old child will have about a
1,500–1,600-word vocabulary.
It is likely she had a fully functional language capability
at the time she was abducted