Psh my excitement is keeping me awake,

Ahem.

Well, the fact that you're actually worried about 'over powering her' makes me more comfortable, because that means you'd still try to find a way to balance her if you went for it. These half breeds aren't initially aware of this power, just that they're rather talented in an area of magic or combat, their talent might even affect their personality in possible adverse ways (hell, they're part demon now, they aren't quite as.. constrained as other people XD)