What can be done to help this?

So you're texting a girl you've been texting/dating/seeing for a while, couple of exchanges and then you start to redirect the conversation somewhere more fun/flirty. I get the feeling it should not be at all difficult, however on a couple of occasions the girls just don't seem to understand why the direction or topic of conversation has changed, or they just don't pick up on the flirting. They seem locked in on the previous topic of discussion.

I have no problem being able to redirect conversational flow both in person and with a majority of people in texts, but sometimes you come up against someone who just doesn't seem to "get it"?

This sounds like a stupid question I know, but maybe someone understands what I'm trying to get at here?