From the moment Sandra Rossi stepped on to the pitch at the Estadio Monumental for photographs with Marcelo Gallardo and the rest of her colleagues at River Plate, she was embarking on a mission that was both life-changing and game-changing.

Her ever-present smile was a little wider that day because a childhood dream was coming true. Rossi was not just joining one of the biggest clubs in South America but her childhood club. She was also becoming the first female assistant coach in the continent’s top-level football history.

That moment, in June 2014, was the launching point for one of River’s most successful periods amid revolutionary input from Rossi. She works with players on the mental side of their game and uses neuroplasticity – in essence training the brain.

Rossi’s hiring by Gallardo, the head coach she had met a year and a half earlier, prompted a great deal of chatter. Working in a male-dominated environment was nothing new to her but questions were asked about her appointment.

“Many thought that I was going to last two months, if I was lucky,” she says. “Many thought that I could not take it; that this was not a place for a woman. Little by little, we got to know each other, we let our defences down and we could rebuild a space where we could coexist and where I was well received and didn’t feel uncomfortable. It is not an easy environment, especially because of the egos. Each one wants to take credit for the successes and that weighs more than any gender.”

Rossi says she has felt no gender discrimination. Her previous experience includes working with the Poland men’s volleyball team and across a variety of sports in Argentina’s Olympic team. She also played a fundamental part in the growth of the Argentina men’s rugby union team over the past decade through neuroscience.

“I am very passionate about my work, so I didn’t find it so weird to work with men,” Rossi says. “Yet from the outside, people would tell me that I was crazy. ‘You are working in football? You’re crazy, you’re going to last two months. You’re out of your mind.’ That was when I realised how big this was and I asked myself: ‘Am I doing the right thing?’”

Sandra Rossi oversees training at River Plate. ‘I am very passionate about my work, so I didn’t find it so weird to work with men,’ she says. Photograph: Diego Haliasz/Prensa River Plate

Within a year River won a league title, a Supercup, a Copa Sudamericana and a Copa Libertadores. Her contributions helped River to the final of the Club World Cup, in which they lost against Barcelona. Not a bad start.

Rossi’s job is not just to “unlock” the brain but to help players manage certain situations and deal with their psychological wellbeing. “It’s only when you are on the inside when you realise how much pressure [players] undergo, even at such a young age,” Rossi says. “Many of us at that age are looking to start college or getting started at a job. The amount of pressure players go through every day is unbelievable.”

In environments such as Argentinian football, masculinity is king. Certain emotions are repressed and players are not taught to handle pressure situations. This is why Rossi deals with the physiological part of the team’s emotional state. “We want the players to be connected and understand the situations they are dealing with,” she says. The squad embrace exercises that will help them to compete and improve. In general, the reaction time exercises are the most popular as the players compete to improve by milliseconds to end up top of the rankings.

After the success of 2015, fatigue has set in at River and this has been a less spectacular season. They have struggled domestically and went out of the Copa Libertadores at the last-16 stage.

That has not stopped Gallardo’s project as he looks to revamp once again. “In the span of a year, we’ve travelled over 150,000km,” Rossi says. “Personally, I take it calmly and without getting too desperate. I try to stay calm and adjust the demands that they can offer. Sometimes overtraining can cause worse effects than the lack of it.”

During the past 18 months Rossi has been able to train the past two South American Player of the Year winners in Teófilo Gutiérrez and Carlos Sánchez. They have been among various players who have left River to go to Europe or Mexico. The players who come in are a challenge for her professionally and personally.

“All the variable metrics that were taken are given to the coaching staff with the purpose of establishing parameters that contribute to knowing the performance and capacity of a player at a deeper level,” Rossi says about her role in preparing a player mentally. “What also happens is that being a woman within a group of 50 men, my role has to deal with the feminine side. We spend several hours together, many of them could be my sons and the bond that we create allows me to know what is going on with them. If they are sad, if they are worried about something.”

Teófilo Gutiérrez, here celebrating a goal for Colombia against Honduras this month, is among the players Sandra Rossi has worked with at River Plate. The forward now plays for Sporting Lisbon. Photograph: Luis Acosta/AFP/Getty Images

Rossi had met Gallardo when he was out of work. He had previously coached the Uruguayan club Nacional, having been appointed shortly after he retired as a player there, and had great success in winning the league title. As soon as that was accomplished he returned to Argentina to take a break and rethink what he wanted to do with his life.

During this time he started to observe the work that Rossi had done with Argentina’s Olympic team as the head of the National Argentine Centre for High Sports Performance and at the Miami-based 1st Place Institute, where she had applied her knowledge of neuroscience for the previous 15 years.

Rossi and Gallardo hit it off. As time went by, they met regularly and learned how each other worked. “One day, during lunch, he proposed to me to join him as a part of his coaching staff should he get the opportunity of coaching a team,” Rossi says. “ I accepted.”

When Ramón Díaz left River in May 2014, Gallardo was tipped to take over. “All of a sudden, and quite unexpectedly, Marcelo’s name was being mentioned throughout every radio station in Argentina as they were reporting that he was going to be the next coach of Club Atlético River Plate – my club,” Rossi says.

She knew her transition had to be quick. “Working with Olympic athletes is like working almost in total silence, when it comes to the infinite amount of work and from the solitude that these athletes, who are unknown to most people, have to endure,” Rossi says. “River is the opposite. With everything there is a media circus, everything is easily judged. If you win, you are God, if you lose you are nobody and all this happens in the same week.”

She was familiar from childhood with the extremes that surround River. “I grew up in a small town 40km from Buenos Aires, but every time that we could go I went with my parents and my sister to see River play,” she says with a nostalgic look in her eyes. She was born in a lower-middle-class family, so outings were few and far between. For the Rossi family, going to the stadium was the most viable option. “Looking back and reminiscing about those little girls that would hold their father’s hand and the stadium was the greatest thing they ever saw. I think that we never imagined that those stairs and those hallways, I was going to go through them as a part of the team.”

Not only has Rossi broken the gender barrier, she has also revolutionised the way teams are being prepared. For her football goes well beyond lifting trophies; it is about being able to improve the life of a human being.

“The moments where I feel a great deal of satisfaction, without a doubt, are when players express their infinite affection and confidence,” she says. “Each one has their own style, from the most affectionate ones that hug me really tight and say: ‘Thanks for what you have done for me’, and even those that send me a message via WhatsApp with some type of smiley face. That’s my biggest achievement, the biggest one of all.”