I used to travel with my godson from the time he was about 14 years old. I was like his surrogate father because he came from a fatherless home. We used to stay at my brothers house in Florida, traveled to L.A., San Francisco, Salt Lake City, New Orleans, Mobile, Houston, Reno, Las Vegas, and many local places near our home. I used to suggest certain adventures and let him choose what he wanted to do. If he couldn't make a decision, I would choose. He always seemed to be satisfied with the result. He seemed to just be happy visiting a new and unknown place and any thing that we did was a learning experience for him.
One of the highlights of our traveling adventures was in Salt Lake City when a store clerk asked me if my godson was my son. I hemmed and hawed and said "No. He's my godson." When we got out of the store my godson said "When somebody asks you if I'm your son, say yes and be proud of it." That made my day.
My godson is now 34 years old and a father and seems to be very experienced in traveling with his son.
We have many fond memories and photographs as momentos of our quality time together.
If she doesn't choose anything, choose something active and exciting, if you can stand it. She may just be happy to spend the time with you.
The Louvre and Stonehenge sound like pretty good choices to me. You'll have a lot of time to spend with each other.