She saved a friend (the father of the red haired bitch elf, and contractor to the elder Phoenix) and lost her "flame", that's characteristic of the Zerdinger Family. Probably made her unable to use Aura. It also got her scratched off the family register.
Honestly it's more like she willingly got scratched off the family register. Yea, she's no longer in the line of succession, but she also left the family, probably from the pain of no longer having her "flame". It's the reason why she doesn't really talk about her school days, even though she has a lot of fond memories from it.
She didn't. She was scratched off the register, as if she had never been a part of the family. They didn't hate her or anything, but that also means her child is no longer part of the family and ahe would have known she couldn't villy nilly go and ask them to let him practice. Well, she did ask, but you could see the result. Had he been a "normal" child, no way he would have made it. He wouldn't have had the skill and battle sense to outmaneuver physically stronger opponents, due to their Mana / Aura, and he wouldn't have had the will to get anywhere near this strong. The mother taught him, but even she thought he's an unprecedented talent or something.
Why would she do this willingly, knowing ot would harm her child's prospects in the future, when she married into another family and lived there anyway?
I forgot… what happened to Leo’s mom? I remember she was a strong hero candidate…