... well that sounds like a well adjusted family.
I'm not entirely sure if it's official prison policy but I would think that she would be denied visitation (or whatever it's called) due to her young age, both apparent and actual. further I would think she would have an uber difficult time killing him when and if she does get in. Prisons monitor everything fairly thoroughly so I would think they would notice she does not show up on cameras or brought something to kill him with, especially if it was metal.
Though I suppose she could wear some sort of locket and reshape it into a shiv, they would not expect something like that to happen so quickly even if they did have a reason to suspect her.
Then getting out would be the difficult step.
All in all I would recommend something shady like the warden being a vampire or at least crooked enough to let her get away with it, her bringing in a toxin/airborne-virus/something that would affect humans but not vampires, or use the prisons "black market" against her father. Say, for example, smuggling herself in as a juvie. Another possibility would I suppose be as a underage prostitute though I would half to wonder, well, how crappy is that
prison to have that
problem. but whatever works for your story.