If she is going to One Direction this may or may not apply as they are there from Thursday to Saturday. If she is going to Luke Bryan it definitely won't apply.
I was thinking of the big Country concert. Isn't that in August? My DD went to Taylor Swift at Gillette last year and the Country concert. Given the traffic DH and I took turns driving even though she has her license. It took me 2 hours just to get down Rt 1 (and that was driving in the breakdown lane).
I told DD that if she went to another concert, we were getting a room at the hotel and she could walk over when the concert was done.
I have stayed at the Marriott near Quincy Adams and it is nice. Parking at Quincy Adams usually fills up quickly on weekdays (as does Braintree) due to Quincy Center parking lot being closed.
I would avoid the aquarium, It didn't impress me at all the two times I went. MOS is nice if your children like science. I believe there are also walking tours of Boston you can join. I have seen them when I take a walk at lunch. I have also seen Segway tours but that might be out of your budget.
. There is a hotel next to the stadium. The Raddison I am fairly sure. My friend who comes home to visit stays there. It is clean, close,and once there no traffic. The next day you can drive to the Braintree T station and head into Boston. It is not a bad commute at all. The subway will take you all over. Get off at park st and take the Freedom trail with a character in costume. When done take a swan boat ride and check ou make way for ducklings statue. Head to the north end and eat pizza. We pizza hop and have a slice at many places. Mos and aquarium are ok but. With limited time I would stick with the freedom trail.