She added in an interview with the Daily Buzz: "We went to the zoo for our one-year anniversary and Fiona was in the window.
"Nick, my boyfriend, and I were waiting in line to get our photo taken with Fiona and I gave my cell phone to someone to take the photo and when I turned back around, Nick was on one knee proposing."
Fiona became the first Nile hippo born at the zoo in 75 years back in January and had a fight to survive after her mother gave birth six weeks early.
"Full term hippos usually weigh between 50-110lbs," the zoo says. "Fiona only weighed 29lbs when she was born 6 weeks premature. She is the smallest hippo to ever survive."
The zoo say Fiona is a "little hippo with a big personality".
"As Fiona continues to grow, the many facets of her complex personality are really starting to show!" they said earlier this year.
"It's fascinating to watch how the different elements of her personality seem to reflect the natural history of the hippopotamus."
