1-3: Alrighty.

4. Essentially, another creature was more or less directly grafted onto her soul, resulting in impurities and instability. This doesn't matter under normal circumstances, but magical energy will cause further instability, thereby dealing a greater amount of damage. While the effects of the base spell would be magnified, certain magic may cause additional effects. 

For example, a fireball wouldn't actually be hotter or burn more, but getting hit by that fireball might cause involuntary muscle spasms, seizures, temporary blindness, etc. Only magic will actually affect her so, so a flamethrower won't do that.