Your friend definitely likes you, but she has a boyfriend, which is why she didn’t accept your date for coffee. It’s that simple. I know you’re looking for some hidden meaning because she flirts with you, but the bottom line of any relationship is behavior, and when she turned you down for a coffee date, albeit nicely and with charm, that was your cue to look elsewhere for a date.
If you want to cover all your bases, next time you’re flirting with her, you can mention to her, “You let me know next time you don’t have a boyfriend, ‘kay?” And just leave it at that. So, if she really is interested in you, and becomes single and interested, she has an in to cue you to her new social status.
But for now, remember that when Freud said, “Sometimes a cigar is just a cigar,” April says, “Sometimes a flirt is just a flit.” The real measure of her interest is a yes or no answer to your asking her on a date.
I hope that helps! 🙂