She came to the zoo in 1991 and was featured as Miss June in a 2007 calendar of hippos.
Photographer Sarah Louise Galbraith took more than 3,000 photos in more than 100 zoos in 33 countries and said
Penelope was her favorite because of her eyes and smile, the News Star reported.
"She was an extraordinary hippo with an enormous personality," zoo officials said in a statement. "She loved opening her mouth for apples and treats and enjoyed refreshing water massages with the big red hose."
She died from a heart condition, according to a necropsy.
The death orphans Monreaux, a 5-year-old hippo that was not Penelope's but joined her as a baby, the News Star reported.
"We are all saddened to see Penelope go," zoo Director Joe Clawson told the News Star. "We will keep our options open for finding a companion for Monreaux."