What does it say about someone that accepts adding their name to a publication without doing any of the work?
No, it is certainly not unethical. You made an agreement at the beginning and you fulfilled it. She thanked you for your courtesy. All is well. The one, perhaps, contribution that she did make was to get you attached to the project idea, from which you will benefit. You are the primary author, in this case, of course. 

There are many reasons for including someone on a paper and not all are benign, but I think this one is. I assume the other person is quite grateful, and maybe even a bit embarrassed. She may even not want to insult you by asking to be removed, since you had the earlier agreement. 

But judging her ethics will get you nothing but trouble.