Depends on her interests. Here are some suggestions.
Denver Museum of Nature and Science. Current exhibits
Denver Zoo (right next to DMNS)
Denver Art Museum. Current exhibits
Denver Mint (mint as in money production)
Dinosaur Ridge (lots of fossils, including some in situ)
Rocky Mountain Quilt Museum
Elitch's Amusement Park
Lakeside Amusement Park
Water World Amusement Park
Denver Urban Farm
If she likes outdoor stuff like hiking, etc.:
Chatfield Reservoir, Jefferson County Open Space, and Golden Gate Canyon State Park have lots of hiking trails.
Garden of the Gods in Colorado Springs (about an hour south)
Red Rocks Park and Amphitheater
Rocky Mountain National Park (about 90 minutes northwest)
For shopping:
Cherry Creek North Cherry Creek Mall and REI in central Denver
Park Meadows Mall in south Denver
Flatirons Crossing in Broomfield (~30 min. NW of Denver)
Colorado Mills in west Denver, Southlands SE of Denver
Very hot weather is predicted. Sunscreen and lots of water is highly recommended!! Hope you have a fun trip.