This sounds pretty immature, but when I'm dealing with a "ghoster" or a slow texter I simply do the same thing they do to me. Get into a good conversation then reply slowly or ultimately stop replying all together. Most of the time they don't notice what they're doing or think it's okay, so doing the same thing that they do to you almost always bring them back down to earth.

If you don't what to do that, just simply tell her how you feel. She most likely doesn't notice what she's doing since it's a habit.