not reading the other posts, this topic can get nasty, so I'll just say my piece.
My 10 year old goes, he says he feels better, but then nothing has ever really been wrong with him.
My 8 year old goes, she's in gymnastics and just made preteam and it's HARD on her body. She messed up her shoulder, couldn't move it, spent hours in the Er only to be told it was fine. Chiro fixed her right up and she had full range of motion after two visits.
My 8 month old goes, he was this tiny little tense ball for a good 6 weeks after he was born. I had a different baby after the first visit, he unclenched and was happier and slept better, cried less.
I can't say I always feel better after going, sometimes it hurts. But my one hip goes out all the time, and I have gotten so I can tell. I start to trip over that foot when I walk. The tripping stops after she puts everything back into place.
So for us there are issues at times but mostly it's preventative and we all like it. I don't always see a difference but when there is a problem I normally do. Some things do take time though, it took two visits for my DD's shoulder to go back right and stay put so she could move it without pain. If your daughter is going to need surgery chances are it may take awhile before you see obvious results.