Rosie Brennan is having one of the best seasons of her cross-country skiing career.

On Dec. 2 she took 11th in a 10K freestyle World Cup race in Lillehammer, Norway. Then on Dec. 16 she placed sixth in the same event at a World Cup in Davos, Switzerland. Both were career bests.

And that’s huge for the 30-year-old Parkite, especially considering her last season, when she went from placing between 15th and 35th place in World Cup events to placing in the high 40s.

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At the Olympics in Pyeongchang, South Korea, she placed 58th.

After the season, she was cut from the U.S. national team.

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It wasn’t until April that Brennan found out she had contracted mononucleosis during the season.

“My symptoms weren’t awful, but my body wasn’t interested in racing,” she said.

Despite that realization, Brennan wasn’t offered a place with the team — a prospect she hadn’t even considered. The idea that she may not be able to compete for the first season in more than a decade, and that the last season could have been the end of her career, was unsettling.

At the time, she didn’t have a plan B. Nor did she have any confirmed World Cup starts, but because Plan A was to race in the World Cups, she started training again.

It was hard at first, since she had to forget about last season.

Last winter she felt fine, except when she was racing.

For the first 2 kilometers, she could keep up with her opponents, then she started to fall behind.

“It was almost like an out-of-body experience,” she said. “Sometimes, my mind gets fatigued, but it wasn’t that. It was just my body. It just wouldn’t go. I mean, horrible feelings and I would just barely make it to the finish line of races.”

She went to see a doctor, but by that time it was January and she was in the middle of the World Cup season, with a spot in the Olympics.

Her blood tests didn’t raise any red flags.

She didn’t feel like she could quit, even if her body wasn’t performing like it should, so Brennan simply endured.

“It just got to the point where waking up to think about going to training was just awful,” she said. “It was a rough place. It’s just one of those situations where you’re in this tunnel and I didn’t want to give into the negative feelings, so I just kept thinking ‘OK if I just rest this week, I’m going to be better tomorrow. Things are going to turn around.’”

Brennan described competing at the Olympics as the worst race of her life.

“I think that was the peak of the mono,” she said. “As I was racing, I was thinking ‘I’m just going to go until my body quits, because it’s the Olympics, I’m not going to drop out of the race.’”

At the same time, she also felt she was damaging her body.

“I did make it across the finish line barely,” she said.

To Brennan, losing her spot on the U.S. team meant she would continue to train with her club coach, Erik Flora, and that she would have to find her own wax technician to go through the delicate process of preparing her cross-country skis for the World Cup series. She would also have to pay for her travel and lodging and race fees.

In summer, Brennan returned to her club, the Alaska Pacific University Nordic Ski Center, and resumed training with Flora.

When she felt like she had returned to health, she signed up for a couple foot races, including the Alaska Run for Women in June.

“I had to have a test,” she said.

The 5-mile run, which raises money to fight cancer, had a turnout of more than 5,000 participants. Brennan took first with a time of 27 minutes, 31 seconds, and broke the course record by five seconds.

It was her first time competing in a foot race since she ran cross-country for Park City High School.

“Not only am I healthy, I’m in pretty good shape,” Brennan remembered thinking.

She no longer doubted whether the virus was lingering, or if she’d done long-term damage to her body by competing while ill.

She said the rest of her summer training season went well, and then a technician with the U.S. team helped her find Karel Kruuser, an Estonian technician, to travel with her and help her through the season.

“I had never met him,” Brennan said of Kruuser. “I knew nothing about him, so I wasn’t sure it was going to work.”

Fortunately, it did, and Brennan has been on a tear ever since.

She hasn’t felt any lingering effects from mono, but just to be safe, she didn’t compete in the grueling Tour de Ski stage race through central Europe.

She will rejoin the World Cup circuit in Austria, and hopes to contribute to a relay medal at the World Championships in February.

Now, she’s setting goals that seemed out of reach just a few months ago.

“We’ve never gotten a medal in an Olympic or World Championship event in the relay, so I would really like to make that happen,” she said.

Even if she is on a team of her own.