@w00dy85 don't listen to the haters. You'd think they'd want the best for their kid rather than screwing them over in order to penny pinch. Absolutely disgusting. She's 11, not 2, there's nothing wrong with her enjoying good hardware and CPUs keep their value so well, and have so much longevity, a 3800x might seem overkill but in reality it's a great CPU to have considering it will last a LONG long time and it costs so little relative to a GPU. Same for overall platform, an X570 might seem overkill but 5 years from now it will still keep trucking and will seem like a great move in hindsight. There's been people holding on to Nehalem for 10 years just fine, and it's not like rate of progress has been accelerating since then.
As for the Titan, yeah definitely sell it if you get a good price. The newer features of cards are a definite benefit and will help her out more. A 1660 Super would work great in that PC for her.