Marilyn Brown's children were in Pantglas school and she lost her daughter Janette, but her son was saved by a teacher.
She said: "I didn't realise he was saved because he'd run up from the school and I had run up to the school, and we sort of passed one another.
"But I didn't think Janette would die. In my mind, she was still alive.
"We stood up at the top by the school, and all the women were together, and I ran from the house."
Speaking to BBC, she recalled that her daughter didn't want to go to school that day, but Brown and her husband told her "you've got to".
She then watched her children walk up the street to school.
"I thought, 'oh, I'll sit down now and have a cup of tea,'" she said.
"I sat down. It wasn't there hardly any time at all, and my nephew run down the street and said, 'you'd better come up to the school... there's something gone wrong.'"
Brown ran up the street in her slippers and remembers being stood waiting for "a long, long time" to find out what was happening.
"We didn't realise then the children had died," she said.
"It's still there. It'll never go away, and I hope people will remember, and they have today."