Ms Mardini is among 43 athletes chosen by the International Olympics Committee to potentially form a multinational team of refugees in Rio.
But it has been a death-defying move from the Mediterranean to training in an Olympic-sized pool.
In the summer of 2015, Ms Mardini and her sister Sarah, 20, climbed into a rubber dinghy in Turkey bound for the Greek island of Lesbos.
Twenty people were packed onboard and “only three could swim,” she said.
When the boat began taking water, Ms Mardini and her sister plunged into the sea.
Each holding on to one side of the rubber boat, the sisters swam with just an arm each, tugging the vessel along.
“It was awful in the beginning but we thought it would be a shame if we didn’t help the people who were onboard with us,” Ms Mardini recalled.
After several hours they finally reached Greek shores at dawn.
“Baba, we did it! We are in Greece!” they screamed down the phone to their father, Ezzat Mardini, 45, who was then a refugee in Jordan.
Mr Mardini has since been able to join his daughters in Berlin, and recalled the nerve-wracking wait for news of their fate.
“It was the longest wait of my life; I was so afraid,” he said.
In their subsequent trek to Germany, Ms Mardini said the sisters drew strength from their life-or-death swim as they faced hostile Hungarian police bent on beating them back to the borders.
“We almost drowned,” she said. “Do you think you can scare us?”
In Berlin, they were given shelter in a former British army camp, where an Egyptian interpreter put them in contact with the local swimming club Wasserfreunde Spandau 04 and its coach Sven Spannekrebs.
‘I want to inspire refugees to live their dreams’
Spannekrebs has been pushing Ms Mardini towards her Olympic goal.
Only five to 10 athletes are expected to go to Brazil to compete, and Ms Mardini is training hard for her berth on that plane.
“I have my best chance in 200 metres freestyle,” she said.
Spannekrebs said: “To qualify for Rio, she needs a time of 2 minutes 03 seconds. Her best time stands at 2 minutes 11 seconds.”
Mr Mardini admitted time might be running out for his daughter to qualify for Rio.
But she could have a better chance at Tokyo 2020, he said.
Ms Mardini’s face lit up when she spoke about the Olympic Games, even if she would not be representing her home country.
“Whichever flag it is, the feeling would still be the same,” she said.
For her, competing in such a multinational refugee team has a special meaning of hope.
“I want to inspire them to live their dreams, just as I am living mine,” she said.
