Explain To Me How…...

Donna became a vampire. Since she was already killed by being stabbed by her bother. She was dead, so how did she become a vampire? Zombies as we all know from the movies are self made, during a outbreak everyone who dies turns into one, but not so with vamps. I’ve seen “Interview With the Vampire” enough to know that you can’t turn anyone who is already dead into one, so there’s that, so that just brings me to my original question, who or what made her a vampire when she should’ve just been “dead”?