The 19-year-old endured a harrowing 15-hour wait before being taken through the floods to the hospital.
Her mother Leona took to Facebook yesterday afternoon to express her relief that they had finally made it safely to hospital.
“Thanks to friends of friends for going to great lengths to get Shan to Texas Childrens!,” Ms Tynan wrote. “She is now on her way with Monica while the weather has allowed a path before more flooding is due later today! So relieved she will be out of danger and can get treatment!
“We are so grateful for all your support! A big shout out to Danny and Charles for getting Shan to the hospital safely.”
Earlier yesterday, Ms Tynan had outlined their predicament to RTÉ radio presenter Seán O’Rourke.
“We’re getting fairly battered by the level of rain,” she said. “It’s noisy, it’s loud, there are alarms going off every few minutes for flash floods, tornado warnings.
“We’re holding onto power at the moment but we have got an email from the apartment complex saying they’re expecting a lot more water to enter the building later on today. In the coming hours, we could be without power then.”
In the midst of the chaos, and unable to reach the hospital 3km from where the family is staying, Shauntelle’s health had begun to deteriorate. She had developed an infection and was in need of a blood transfusion.
Without a transfusion, Ms Tynan said, “she will only get worse”. The family had called emergency services a number of times, but were told they were “dealing with thousands upon thousands of people that need to be rescued everywhere and they’ve limited resources”.
Shauntelle, her mother, grandmother, and two younger siblings, aged 11 and six, were trapped on the fourth floor of an apartment complex, surrounded by at least five feet of water, with more catastrophic flooding forecast.
She was diagnosed nearly two years ago with a rare form of multi-system Histiocytosis X/Langerhans cell histiocytosis.
Since her diagnosis, the cancer has spread to her gastrointestinal system, colon and skin.
Shauntelle set a record for the most successful appeal for money for cancer treatment earlier this year after online posts went viral.
She raised more than €700,000 to allow her family to cover at least a year’s potentially life-saving care in Houston.
Shauntelle has been told by her Texas-based doctor that her chances of recovery depend on how long she can spend in the US.
The Tynan family were given financial assistance for the trip by The Gavin Glynn Foundation, a charity set up in the memory of four-year-old Gavin Glynn who died in 2014 from an aggressive form of cancer (thegavinglynnfoundation.ie)
Meanwhile, it emerged last night that 30,000 people in Texas are in shelters as a result of the damage caused by the hurricane.