Do you talk to her already or are you friends? If not, I would start by just building an acquaintance and casual friendship with her, slowly (think, chatting/messaging once or twice a week to start with).
You want to avoid giving her too much attention because that might make her uncomfortable: 1. Because she's probably very emotional after her break up, and 2. Because giving her too much attention and pursuing her too hard will make her feel like a piece of meat or an object that you're trying to attain as soon as she becomes available (and especially after her breakup when she feels vulnerable and may be an easier target)
Go slow - if she finds a new boyfriend while you're slowly trying to build a friendship/relationship with her, then she wasn't very interested anyway, so you're better off not having tried too hard. And trying too hard will probably scare her off anyway