Kirsten is playing the swimmer, who grew up in Brighton, in the film Vindication Swim, written and directed by Brighton-based Elliott Hasler, aged 19.
Filming began last June, originally with the hope of completing the film by spring 2021 in time for the key festivals. However, lockdown put everything on hold.
Work has now resumed with shoots in Eastbourne and Amberley. The hope is now to release the movie in summer 2022.
It has been a long process already, with the director preferring to film seasonally, Kirsten says: “If it is supposed to be in winter, he wants it to look like winter with no leaves on the trees.
“Also we tried to do all the swimming scenes in July and August. Sometimes I was in the water for about four hours at a time, and for health and safety, you had to keep to the temperature guidelines.”
During lockdown, the team tried to do whatever they could: “We tried to do scenes where it is just me in isolation – or we were working on post-production or working with the music.
“We were trying to do some of the things that are usually done at the end of the project just to help things not to slow down so much, but obviously everything has slowed down.
“But I always try to be positive, and the positive about having time away is that you don’t usually have time to reflect on what you have done so far.”
As she says, lockdown gave her the opportunity to reflect on her performance and to try to breathe new life into the next stages of the project.
“Also when you are doing a biopic or a historical study, you have to keep referencing back to the history of the period – which can be quite difficult when you are filming. This pause has allowed us to look back at the finer details of the period.”
Of German immigrant parents, Mercedes grew up in Brighton, but her parents, despite their years in Brighton, had never sought British citizenship.
Her father was interned when World War One broke out, and her mother, though she was permitted to stay, opted to return to Germany with her children, including Mercedes. Mercedes decided she wanted to be in England and tried to swim back at the age of 17 – an attempt which fuelled her Channel-swimming ambitions.
“She had a real natural talent and decided she wanted to become a professional swimmer. She had bouts of bronchitis and she was very small. She didn’t have the really big swimmer’s build. But she decided to swim The Thames and then from there she decided to swim The Channel.
“It took her eight attempts before she managed it, and she paid for it all from her own wages.
“After the Channel swim she went on to do lot of other swims, and she became quite well known. She did shows which helped her pay for her next swim.
“She was the first ever person to swim the Gibraltar Straits which is a really, really dangerous swim.
“But later in life she became quite a recluse. Her daughter said she was a person who liked to live in the present and didn’t mention her swims while they were growing up.
“For me, I think it is really important to embody her passion for open-water swimming.
“That alone makes her so beyond her time. To be a female athlete in open-water swimming in the 1920s was quite a rebellious career really.
“But she really, really embraced her need for swimming and her need to succeed in it. And for me that is the challenge too.
“I am quite a good swimmer, but I had to have about two months’ full-on training before we started.”