My 12 year old daughter just finished building her own PC and only came to me a couple of times with questions but I never actually touched the thing. She did it all herself including sourcing the necessary parts within the budget I gave her. She even painted the outside of the case herself with her own artwork!
I have a few friends which are girls, that build their own PC's. Although recently one of them decided to go with Alienware, due to timeframe situations.