When Haley Matheson was 15 years old, she received news that no teenager should.

A little over a year ago, she became sick with what she thought was strep throat, but in only a few weeks her symptoms escalated into something much more serious.

She started losing vision in her left eye, experiencing fainting spells and breaking out in rashes.

"When I started to get sick it was just really scary," Matheson said. "We don't know what happened, we don't know how it came on. All of a sudden, I'm sick. I'm really sick."

Her mother, Marion McPhee took her to the Queen Elizabeth Hospital in Charlottetown, where her blood work showed that Matheson had almost no white blood cells, low platelet counts and that her hemoglobin was critically low.

She was immediately transferred to the IWK Health Centre in Halifax where a team of specialists was able to give her a diagnosis.

Matheson had aplastic anemia — a rare disease that causes deficiency in all three blood cell types.

Doctors told Matheson that her best chance at survival was a bone marrow transplant. Neither her mother or father were a match for donation.

That's when Matheson's 11-year-old brother, Reece, volunteered to be her donor.

After Reece tested positive as a match for donation, he travelled to SickKids Hospital in Toronto where he stayed in the Ronald McDonald House to wait as his sister prepared for the surgery.

"It was so fast. I was pretty emotional, didn't really know what to do, just did what the doctors told us to do," McPhee said. "It all was real, we almost lost her."

McPhee said doctors told her that there was a 25 per cent chance of full siblings being a match for bone marrow donation.

"Only having the two children, we were really lucky."

Matheson said she was grateful when she heard her brother was a 100 per cent match and volunteered to donate. She said that she was given an 85 per cent chance that the surgery would be successful.

"Mine worked perfectly because I had a sibling donor," Matheson said. "I'm just so grateful because he could have said no, he didn't have to do it. But he chose to."

Reece, who is now 12, said he watched for weeks as Matheson underwent dozens of tests, several blood transfusions and chemotherapy during her time in the hospital. He said he was willing to do anything to stop his sister's pain.

"I was very scared, I didn't know if it would be able to work," Reece said. "I was afraid for my sister, I wasn't scared for myself."

The siblings both underwent their transplant surgeries in February of last year. Once the surgery was over, McPhee said both siblings recovered quickly and without any major complications.

"He walked right out of there like nothing happened," McPhee said. "Five hours later, walked out of the hospital."

Matheson said the disease has left her with a weakened immune system and she still has to take several medications to stay healthy, though her last few check ups with the doctor have gone very well.

"I'm just so grateful for everything," Matheson said. "Life is so precious and I took so much stuff for granted and it just shows how important everything is, even the little things."

Matheson said her health has improved enough that she was able to return to school last week for the first time since the surgery.

She said the experience has taught her the importance of not taking anything in life for granted, especially her little brother.

"I'm still here, that's what you need to be grateful for," Matheson said.

"Now matter what's going on around me, I'm alive."