United Center in Chicago

I'm guessing you'd like to stay in the areas close to the tourist stuff, so stay on Michigan Ave, and take a cab to the United Center (and a cab home, they'll be a ton around after the concert).

The others are right, there's no hotels over there, and nothing else that you'd want to do. So don't center yourself around that.

Take the Amtrak in, and take a cab to your hotel. (I like either The Allerton, which is right next to Water Tower, or The Omni, which is right in the middle of the Mich Ave.)
Make sure to check for street festivals and get out of the tourist areas, though. The real feel of the city is nowhere to be found on the mag mile! :)
Go to Wrigleyville, Lincoln Park, Bucktown, and Lakeview (I'm happy to make bar suggestions, if you're going that route).
Oak Street beach will be walkable from Mich Ave in June, and if the weather is nice, the lakefront is beautiful - especially down by the Museum Campus!

Oh man...now I'm just longing for summer.

i live downtown and i would say do NOT walk around the united center. also, the bus line that runs there is sketchy and so is the El. take a cab! You will have to pay a bit, but your safety is worth it. Are you going to the NKOTBSB shows?

K.M.'s hubby is right, the United Center is not really near any decent hotels, or anything else interesting to a tourist, it's not a safe area to walk around if you are not familiar, and it's a few miles from the Amtrak station. If proximity to the event is very important, there is a Marriott across the street from Rush University Medical Center at the intersection of Ashland and Harrison. It is several blocks from the United Center, but a very quick cab ride (I would not recommend walking). That area (Medical District) is pretty safe, and you'll have access to the El to get downtown easily. Otherwise, you may just want to stay downtown somewhere, where there are tons of hotels to choose from and you will be much closer to the fun stuff.

As far as MUST see, there is a ton to do in Chicago, especially in the summer. There will likely be several festivals at various locations throughout the city. Popular tourist spots include the Willis Tower, Magnificient Mile shopping, Museum Campus, Hancock Tower (go have drinks at the Signature Lounge on the 96th floor, you get the view without having to pay the price for the observation floor, and won't have to deal with tons of children running about), Millenium Park, Buckingham Fountain, etc. etc. etc. There is a lot to do. If you want to do it all, there is a pass you can buy that includes admission to all the hot spots for a discounted price than buying each separately.

Hope you have fun planning your trip!

As everyone else said, take a cab to the United Center. Hotels in the downtown area are your best bet to be near the tourist areas, but if you want to stay a little closer to the United Center, there is the Marriott someone mentioned (right near the University of Illinois at Chicago campus) and there is a Crown Plaza in Greek Town (at Madison and Halsted). There are so many wonderful things to do in Chicago that you'll have to pick and choose what's of most interest to you to do while you visit. Navy Pier, Millenium Park, museums (Art Institute, Museum of Contemporary Art, Field Museum, Shedd Aquarium are all great choices but there are so many more), shopping on Michigan Avenue, Buckingham Fountain, John Hancock or Sears Tower (I know its called Willis Tower now but I'm a Chicagoan and can't call it that yet). My suggestion is to say more in the "Loop" area than the Magnificent Mile you will be a bit closer to the United Center (still need to take a cab there) but walking distance to everything else. Do a search on hotels.com or another travel site and you can see a map of where the hotels are compared to the various attractions. Have fun in beautiful Chicago! It really is a wonderful city to visit, especially in the summer.

Stay on Michigan Avenue. Take a cab to United Center. (It will take about 10-15 minutes.) Check out Navy Pier. It's beautiful and fun on a nice summer evening. There are boat tours that take you on the Chicago River and they do a great job of showcasing the city that way. They also go out onto Lake Michigan so you can take your own postcard pictures of the skyline. Shedd Aquarium is a great place to visit. While there you can also see the Field Museum and Adler Planetarium (and take a look at Soldier Field) and have lunch on the lakefront. There is great shopping on Michigan Avenue and you should try Uno's or Due's or Gino's East for some Chicago-style pizza. And go down Michigan Avenue to Millennium Park to see the Cloudgate sculpture (informally called the Bean) and hear some live music and see the cool water sculptures there. Have fun!!!

Chicago Guru Hubby says

The United Center is far from Union Station and there are no hotels nearby because it is in the middle of what used to be (and still kind of is) a ghetto.

there will be taxis but she should stay in River North

The problem with United Cente ris that it is literally not near anything else interesting to people who are just visiting for a weekend