i guess she died bc of both?... She already suffered from the burden of taming a dragon and she casted a spell that has a lot of backlash on the caster on top of that, leading to her death I assume
She would have lived if she had released the dragon and any other that consumed mana when she was going to use that spell, but no one thought she'd die ┑( ̄Д  ̄)┍
( ̄∇ ̄") Didn't he first say that she died because she tamed a dragon and now it's because she used a spell(╯°Д °)╯╧╧