Helene Campbell, the 21-year-old Ottawa woman recovering from a double-lung transplant, is back in hospital after experiencing shortness of breath.

A blog posting late Wednesday by her mother, Manon, reveals that Helene was readmitted to Toronto General Hospital on Sunday night – just a day after being discharged following the surgery. She returned to hospital because she was feeling short of breath while walking as well as at rest.

For the last three days, Campbell has been undergoing tests to help determine why she has been unable to get enough oxygen and to help her doctors and respiratory therapists decide what to do next, Manon writes.

Infection and rejection remain major risks at this stage in her daughter's recovery, she noted.

"Transplant is not a cure; it is a treatment, and like many treatments, there may be adjustments, side effects, complications, and lifestyle modifications as part of the picture for a transplant survivor," Manon wrote. "Once we understand this, it is a lot easier to accept the humps and bumps on the road."

She also noted: "We are very thankful for the fact that we had most of the weekend together - we also know that there will be many more to come."

"While waiting for more tests and results, Hélène's attitude remains strong and positive," her mother wrote, noting that her daughter's medical team expects her return to her Toronto apartment will be "sooner rather than later."

Campbell developed advanced idiopathic pulmonary fibrosis last September, and received the double lung transplant at Toronto General on April 6.

She captured the hearts of Canadians when she began using social media to find a potential lung donor. She first got her message out through a tweet to Justin Bieber asking him to spread the word. He re-tweeted it to his more than 16 million followers.

When she then sent in a video to the Ellen DeGeneres TV show about the need for organ donations, DeGeneres put her on her show through a Skype interview. DeGeneres has invited her to return to the show after the lung transplant.

Campbell's Twitter account has more than 15,000 followers with people from around the world following updates and cheering her on.