The protracted race to qualify for Glasgow 2014 ends with a final sprint to the wall this weekend with the North District Grand Prix, which begins tonight at Aberdeen Sport Village, offering one last opportunity to obtain qualifying times.
Already 40-strong and the largest Scottish aquatics team ever sent to a Commonwealth Games, a handful of vacancies remain unfilled. Johnstone, with her berths in the 50m and 100m backstroke secured, could potentially chase a spot in the 100m freestyle at the meeting. However, the 23-year-old from Dunfermline - who was a finalist at Delhi 2010 - believes the impact outside the pool of any success this summer is a perk that must be capitalised on.
"Especially the last couple of years, with Scottish Swimming doing lots of live web streaming, it's attracted more people to watch who haven't come to the pool," she said.
"I've got a friend with a kid who never really thought much about swimming. But now I've had her asking me: 'how did you start off or how can I get her into it?' I get updates on how she's progressing and it's nice to know you are having some impact."
Johnstone, who will be joined by Ross Murdoch, Robbie Renwick and Hannah Miley in Aberdeen, has given her backing to Scottish Swimming's Everyone Can Swim campaign. A Games in Scotland will inevitably breed new role models, an adjustment that might take some time.
"I went to a competition in France once and I was just standing around when a little kid came up and said: 'can you sign this?'," Johnstone said. "Once one person saw me sign something, then there was a massive queue coming over who were clearly thinking I must be a big-name swimmer. It was a couple of years ago when I wasn't particularly good."