I quite agree! So it seems the challenge for you is how to be friendly (courteous/cordial) yet keep the relationship within professional parameters. This means that you cannot engage in any of the activities that you would avoid outside work, like listening to her personal problems.
It is a good idea to take your breaks. Can you take them somewhere else, or at a different time than she does? Run an errand? Sit in your car?
You have misled her, albeit unintentionally. You may have been clear with your words, but your actions are opposite. If you listen to her personal problems, you are crossing from a professional relationship into a personal one. Asking you to bring a souvenir is evidence of that. Her knowing you are taking a trip is also evidence of that.
No one is saying the advice had to come from the boss. There are other places that people receive guidance in life. Perhaps you can be creative and come up with something else to say that will help you set and keep the boundary you need.
It will be awkward for a while, but if you are consistent and repetitive, it will eventually work. This is the main function of polite excuses.