One of the CPS documents posted by CM at KHOU mentioned that Maleah had been doing physical therapy and OT (probably beginning in the hospital) and "would soon be in speech." She would have been entitled to these services as a result of of her surgeries and injuries and it means SOME delay had been documented. It's somewhat unusual for a child to get speech services before kindergarten (more common for a child who has had contact with medical professionals though), so her speech issues or delay was probably fairly significant for a 4-year-old. This might have meant she didn't speak much and/or that she was hard to understand (either of which could have been related to the brain injury or to being raised in a household with several risk factors for delayed language development).
If she had become more verbal recently, that could explain why DV and others were more worried than they used to be about what Maleah might say to teachers, doctors, caseworkers, etc.