My DD wanted longer hair, as well, but I told her that in order to have long hair she would have to take care of it (or allow me to)... which meant twice daily brushing/detangling, and it would take longer to shampoo, etc. This lasted a few months, we started arguing about it every day, next time it was haircut time we cut it back into a bob. She was happy to be done with arguing and I think its much cuter on her face anyway.
DD2, age 2 1/2, is only just getting enough hair to make this decision. She actually likes "ponies and clippies" so I'd be inclined to keep it longer but she is starting to argue the combing out too. I think we are going to shorten it a bit (her first real haircut!) when we do "before-school cuts" but not go quite as short a bob as her sis just yet.
We all have responsibilities from choices and I see having to comb out hair as one of those. You want it, you need to take care of it.
Paul Mitchell detangler is awesome, btw, expensive but better than others I have tried.