Your daughter is at or getting to the age of puberty which is most likely the reason for the change in her hair. There is no miracle to making hair grow or to thickening it. The best thing you can do to keep her hair healthy is to make sure she takes a multi-vitamin everyday, have her drink 8 glasses of water (which everyone should to wash the toxins out of your body), and to eat a healthy diet. As far as products, you get what you pay for. I personally recommend Aveda which you can only purchase at high end salons. Since her hair is fine, it would best to not perm or process her hair in anyway. Salons sometimes encourage processing, however they do it for the $$$. The processing will make her hair more brittle and dull! To give her hair body, use the simple trick of putting a volumizing mousse in hair while damp, then blow dry upside down.....making sure to dry the roots, and also wait until hair has cooled before flipping it back up. Try not to get the ends dry while doing this. You will want to finalize the drying period with a round brush and blow drying if you want volume and curve in her hair. I also recommend that you take her to a hair school and get her a scalp treatment. This will thoroughly clean her scalp, manipulate the blood flow, and leave her hair very clean yet healthy looking. The reason I said to go to a school is because it is very cheap, and they are as good as we are at doing the treatments. Please leave a tip because that is the only money that the students make at the school:) Hope this helps.
God Bless,
Teresa