Cook, 44, was part of the Great Britain eventing team that confirmed their spot in Rio by claiming a silver medal at the Alltech FEI World Equestrian Games in Germany last year.
Despite the team qualifying, GB eventers now face a gruelling year as they try to stake a claim by gaining individual qualification.
Cook knows she faces a tricky season, with the Badminton Horse Trials in May, before the European Championships in Scotland in September.
The Findon eventer is hoping she can do enough to book her place in the team that travels to Rio next year.
She said: “This year is going to be a really tricky one, with everyone vying for that individual qualification for the Olympics.
“It was great to be part of the side that took silver in Germany last year but that just means that Great Britain will be at the event and the hard work starts for me now.
“Being involved in an Olympic Games is magnificent and I have been fortunate enough to win medals in the last two.
“I’m hoping I can produce some good displays this year and really stake my claim to be in that side.”
Cook competed on her home-bred horse, De Novo News, at the World Games last year, after Miners Frolic was forced to retire owing to a heart condition.
Cook will once again be riding De Novo News at Badminton but is unsure whether that will be the case for the European Championships later in the year.
She added: “I have a couple of other really good horses that are coming up at the moment.
“I was really pleased with how De Novo competed in Germany in what proved to be some really difficult conditions.
“But this year is about finding a partnership between myself and a horse and, once I manage to find that, hopefully I can really push to get into that Olympic team.”