At 11 months old, Hailey Joy Kent has faced more danger than most people do their entire lives. More is coming.

The Simi Valley twin with blue eyes, two teeth and a tendency to snore softly has been on chemotherapy since she was 3 months old. But the treatment hasn't stopped an unusual, aggressive form of leukemia.

Thanks to an anonymous donor's umbilical cord blood, Hailey will undergo a stem cell transplant later this month at Childrens Hospital Los Angeles. The risks are very high, but the operation gives her a chance to beat a disease that is otherwise fatal.

"She's a pretty tough little girl," said Hailey's mother, Maria Kent, biting off the words as she tried to explain how the family is managing. "Just don't have a choice. Just doing it. Just believe she'll be OK."

Hailey's story has been different from the start. Maria and Rick Kent, who have a 21-year-old daughter named Heather, went through nine miscarriages as they tried to grow their family. Finally, a surrogate carried the embryos that produced Hailey and her twin brother, Ryan.

Ryan is healthy, but Hailey's problems began when she was 3 months old. She started vomiting and developed a fever that wouldn't go away. Rushed by ambulance to Childrens Hospital, she was diagnosed with acute lymphoblastic leukemia.

The disease makes some of the body's white blood cells malignant, spurring them to grow uncontrollably.

"They oversuppress the other blood cells. They crowd them out," said Dr. Neena Kapoor, director of the clinical bone marrow transplant program at Childrens Hospital. "It's like a wild weed. You have to take them out to allow the normal cells to grow."

No one in her family, not even her twin, had bone marrow that was enough of a genetic match. But a national registry found umbilical cord blood that matched four of six characteristics not perfect but acceptable.

"They're telling us that with cord blood, you don't need a perfect match," Maria Kent said. "They can't keep searching. She doesn't have time."

Hailey is going through pre-transplant procedures that include a bone marrow biopsy and scans of the brain, body and heart. She will be admitted on May 21.

She will be isolated in a sanitized, sterile area and be given a nearly lethal treatment of chemotherapy intended to wipe out the diseased blood cells. Stem cells from the donated cord blood will be transplanted into her body so they can create new healthy blood cells and rid the body of leukemia.

The aggressive chemotherapy brings with it a heightened chance of damage to the liver or kidneys. But one of the biggest risks is infection brought on by a depleted immune system.

"They wipe you out completely," said Maria Kent. "That's why it's so dangerous."

The transplanted cells could reject their new surroundings, or Hailey's body could reject them. There's also a chance the leukemia could come back.

The family has also been told that her growth will be stunted and that as an adult she might not be able to have children. Her blood type will change from O negative to B positive, and she will need transfusions.

The family copes by praying and taking one step at a time.

"You just remember to breathe," said older sister Heather.

Her mother talks of how much community support and groups like The Leukemia & Lymphona Society and the LightHouse Christian Fellowship in Newbury Park have helped. She thinks about the day, maybe four months from now, when Hailey comes home from the hospital.

"I'll be glad when it's done and she can just do normal things and play with her brother," she said.