read some books, read about current events, learn about other cultures, learn about any kind of shit, engage in a new hobby. ask what she's into and learn about that. talk about ideas. talk about abstract shit. 20mins a day and you can do any of these things. even if you weren't doing this for this girl, becoming a dynamic/well-rounded/worldly person has no downside.
surely you've had friends/people who can only talk about one thing you don't know much about, and know damn well it's annoying. let me tell you how many times i wanted to smother my co-worker with a trash bag when all he talked about was world of warcraft for every agonizing minute of a 2-hour ride.