YA book where the main girl can pause time, read around 2010

[Bree]

I read this around 2008-2012. I remember one of the ending scenes in the book and I’m dying to figure out what the book was. I remember that the main girl is able to like pause time for a couple seconds at a time. The love interest has an old ex that’s is pissed that he is with a new girl and she tries to fight the main girl by turning into a dragon (if I’m remembering correctly). They are inside a large house/mansion and the main girl uses her ability to pause time for a couple seconds in order to evade and fight this dragon. At one point, they go over the banister and are falling to the first floor, I remember that the girl thought something like “this is going to hurt”. But she uses the time pauses to make sure that she falls where she needs to so that the dragon falls onto a chandelier. I also think I remember that during the fight the dragon lady started to become aware that the main girl was pausing time.