Thing that bothers me here is that we haven't had ACTUAL progression. Like, at the beginning she didn't care much about him, that was obvious.
Then she got the drawing from him and blushed a little. Starting there, she was a bit interested.
But this "Suki da!"... She doesn't blush upon realizing what she said, so... Either she REALLY is that dense (and we know she is, but come on...), or she's full-on attack mode now, which is quite the leap.