Diehl became an instant social media sensation, with about 10,000 tweets regarding her appearance.
"Finally, a contestant that's not a bag of bones," one admirer tweeted. Another wrote, "Dear Miss Indiana, thank you for looking like an average woman."
"I was blown away. Never in my right mind would I imagine this would blow up to what it is," Diehl said in an interview on ABC's "Good Morning America."
Diehl is not supermodel skinny, but she is certainly thin. She is 5 feet 8 inches tall and wears a size 4. The average American woman is 5 feet 3 inches and wears a size 12 to 14.
Diehl doesn't view being called "normal" as a backhanded compliment.
"I wasn't being called fat. I wasn't being called out of shape or ugly. In this regard, normal is a good thing," she said.
Diehl became emotional talking about her experience at the pageant.
"It warms my heart to know that I can, just my 30 seconds on stage has touched so many girls' lives and even boys, as well," she said.
Diehl, a self-proclaimed tomboy who played volleyball and ran track and field, said she didn't go overboard in preparation for the pageant.
"I didn't starve myself or go to crazy extremes to get ready for the pageant," she said. "I lived a healthy lifestyle and trained just a little harder, like an athlete, to get ready."
Diehl said she hopes her appearance was an inspiration to girls.
"You can't worry about the girl standing next to you, because you'll never be that girl. Your body is a gift, and you have to love it and have that confidence because that's the only thing you can do," she said. "You can't worry about being somebody else."