I agree with divine that it was a bit too much. On the other hand, this baker chick seems a little awkward and diffident, and that's something you ought to take note of for future interactions. If you tell her, "I’ll get you a hanging plant to put outside your store," she's probably not going to voice her actual feelings for whatever reason. Instead, ask her if she would like you to get her a couple of plants. You could even feed her some line about how your cousin sells plants out of her greenhouse, and you can get a couple for really cheap.

I'm assuming you've already responded to her question about the cost. So, what was the cost? And what did you tell her the cost was?