...has been Belle's best friend since they were kids. They built that friendship out of the hardship of being the victim of the same bully when they were kids, and that friendship lasted into the current day, where they share an apartment together.

She's always known about Belle's love of all things Vampire, and was fine with it even when it got dorky. She laughed it off when Belle swore a guy she was attracted to was a vampire. She wasn't laughing when Belle came home the next day...

Kristy was making out with her boyfriend on the couch when Belle busted in lost in a thirst for blood, took him into their bedroom, and proceeded to commit what was known as "The Sex and Slay" by vampire hunters. She knows this because after she kicked out a remorseful and crying Belle, she learned about a vampire hunter and sought out his knowledge to get revenge and kill her now former best friend.

Meeting Simon did not go as planned, and after he (along with Vincent, whom no one knew was a vampire) tried to get her and Belle to kill each other, she found herself back where she started:

Having her former best friend's back, because she needs Belle to have hers.

Kristy's adventures have found her and Belle discovering it was possible for a Vampire and Vampire Hunter to coexist when they met Syd and Pierce, a vampire/vampire hunter romantic couple.

They trained under the two of them for a while, up until Belle suddenly developed her fangs, right at the moment The Dracula rose from Her 100-year slumber.

It happened while they were sparring against each other, and the chain of events right after simply fell into chaos. Belle, who had been so horrible at using her vampire powers with any success, suddenly mastered "Glammer" and put Kristy into an obedient trance...

...she woke up to discover that Belle had taken Kristy to her "Mother's" house: The Safehouse where The Dracula, The First Vampire, was hiding out since waking.

Now, Kristy is the only human in what amounts to the Royal House of the Vampires.

Good luck, lady.