Demon's Daughter

Sixteen year-old Emily Carson is an average nerd with three goals in life – acing her school exams, dealing with her brother Seth's questionable taste in girls and curing school hottie Adam Farlow's questionable eye-sight (the only explanation for his lack of interest).

And then her Dad shows up.

Discovering that your Dad is a demon certainly makes life much more interesting but even Demon Lords have enemies and Emily and Seth soon find themselves the new targets for every Vampire, Demon and Were in town.
Having Fallen Angel Sariel as a body guard should help but Emily is fast discovering that Fallen Angels can be very tempting indeed.