There is an infinite number of topics you could talk about! Just make sure you keep her laughing and insert a few mini-DHV stories.
e.g. once you've opened and got a positive response, you could move into something like this...
"So how was your weekend?
Mine was a bit crazy..." Then add a mini-DHV story about your weekend.
An example of a DHV story would be
"Tried a new club with some friends. It was cool, but I had to spend most of the evening protecting my friends little sister from being hit on by sleazy old men! This one guy, must have been 45, said he'd buy me a drink if I persuaded her to dance with him. I said no, but only because I was holding out for a pack of peanuts too.

"
In later messages you can ask interesting questions (e.g. So which is sexier, pirates or ninjas? I need tips for a fancy dress party this weekend!), do mini-roll plays, ask her what music she is into etc.