L.O.
I never got into dolls until my sister was about five. I bought ceramic heads and hands and feet, and made dolls(not having a kiln made making my own not possible, so I repainted and created and put elaborate wigs on the heads. My mother being a tailor, I guess crafty rubbed off on me. We had those cabbage patch dolls, and my mother and I made clothes for them. I still have mine(preemies, which is very ironic, considering my son was a preemie), and my son plays with them, and a friend gave me hers, which he plays with on occasion.
On the subject of American Girl dolls, they are made better, with better materials, but until you know if it will be a fad toy or not, I'd say go knock-off...you can get her doll a "best friend" later. Most dolls hair are rather easy to take care of(I can speak of it, because I have made dolls before).
Remember that this type of doll is a HUGE investment. They are more or less intended as heirloom dolls, like the Bébé Bru were in the late 1800's. With the advent of cheap plastics and resins, dolls like AG were possible, as it is cheaper to make, and less fragile than their predecessors.
On the subject of matted hair:
My friends girls Barbies got matted all the time(and we all know how cheaply Barbie's are made). I did this simple trick. I removed them by using a bit of cooking oil in them, then gently combing them out. I then took woolite or a gentle soap like the baby soaps, then washed the hair. After that, I towel dried the hair, and combed it out to remove any additional tangles. Once completely dry, we styled them as normal.
Luck to you!