Firstly, I agree with the others here, your little angel is not possessed. She has some kind of issue, to be sure, but it's a physical one, not a spiritual one. My daughter had many of the same problems and has been diagnosed with having auditory processing issues. She too is of above intelligence, but often expresses herself, both verbally and in writing in a very slurred and jumbled manner. The information goes in, and her comprehension is very high, she is a very discerning young lady, but when she tries to get things "out", it sometimes sounds backwards. Your little one is still young, but she might struggle academically as well, for our written expression is often tied to our verbal expression. Just give her lots of love and encouragement, and especially stress to her that this doesn't make her dumb or stupid.
The idea that every physical ailment or even character failure is a "demon" isn't Biblical. I do know that there are some who believe that alcoholism is an actual demon, that "deaf and dumb" is an actual demon. But, there is just no Biblical support for that. Demons are angels, fallen ones to be sure, but nonetheless of the same nature and with the same abilities as the ones on God's side.
Secondly, why would the Holy Spirit talk to this woman about your daughter? You are a Christian, you have the Spirit. Why the run-around? God placed you as your daughter's mother, care-giver and guardian. Why would He go to others about something as important as this? It doesn't make sense that He would tell someone else instead of you, the person whom He put in charge of her.
Usually, if something doesn't make any sense, it's because it isn't true.
Now, I do believe that children, once having lost innocence, (who knows when that is, it's a very individual thing) can be possessed, or at least demonically oppressed. But, not Christian children, and especially not children who take joy in Christ (even if He's a bad cook!) ;)