~Can she drink blood from your character? Sure. But Magnus is a warlock, and in his world, that means he's half-human and half-demon. So whether or not his blood tastes good is a different story completely.
~Can she transform into your character after drinking their blood? Maybe for neat plot-like purposes sometime? But it'd definitely have to be discussed.
~Can Diva give your character her blood? He wouldn't willingly take it. But, again, maybe neat plot purposes.
~Is there anything that you want me to avoid talking about? Nope! I'm good with everything.