My 11 y/o sister has recently shown an interest in learning maths and I feel like this is a great opportunity to take that interest much further. She doesn't like being taught it at school but has asked me multiple times to explain some mathematical concept to her, and if we have to take a break from it she always comes back on her own asking when we can resume. Though I'm sure a small part of it is an excuse to spend time with her cool older brother, from the way she gets all exited when something clicks makes me think that there is some serious potential in her and I'd regret it for the rest of my life if I didn't at least try to unlock it. Autistic traits run in the family which could further enhance her potential, and there are much worse things to get hooked on.
How should I approach this? Should I just find some textbooks from our local curriculum and just go through it with her? Or should I take a more direct route to something slightly more advanced that interests her and let school fill in the gaps? Lend me your wisdom /sci/.