(CNN) — It was Rosy Esparza's first trip to Six Flags.
She sat beside her son on the Texas Giant -- a 14-story-high roller coaster that boasts what the amusement park calls "the world's steepest drop." And before the ride's cars started moving, witnesses told CNN affiliates, Esparza was worried.
To her, the lap bar that holds passengers in their seats didn't seem secure, the witnesses said.
Minutes later, one of the roller coaster's seats came back empty.
Now Esparza is dead, family members told CNN affiliates KTVT and WFAA. A spokeswoman for Six Flags Over Texas says the theme park is committed to finding out what led to the woman's death on Friday. And authorities are investigating.
CNN has not been able to reach the family for comment.
In Facebook posts on Saturday, her sons described the experience as a nightmare.
A flood of condolences and prayers poured in.
"Only God knows Mama," Amado Esparza posted in Spanish along with a photo showing a group of people praying at the amusement park, "something that I will always have as a memory of you is that you loved adventures."
Later, he described his mother as his best friend.
"It is sad to lose my mom," he wrote, "but I am happy that when she was alive she enjoyed it to the fullest. I always took her to explore new places."
On Saturday, authorities said an initial investigation showed no sign of foul play in the woman's death.
"At this point of the investigation, it does not appear there was any foul play or criminality associated with this tragic incident," the Arlington Police Department said in a statement.
Park visitors told CNN affiliate WFAA they saw the woman fall.
"She goes up like this," Carmen Brown told the affiliate, raising her hand up in the air. "Then when it drops to come down, that's when it released and she just tumbled."
Brown told the Dallas Morning News that the woman had expressed concern to a park employee that she was not properly secured in her seat.
"He was basically nonchalant," Brown said. "He was, like, 'As long as you heard it click, you're fine.' Hers was the only one that went down once, and she didn't feel safe. But they let her still get on the ride."
Six Flags confirmed that a woman died Friday while riding the Texas Giant roller coaster, but did not provide further details.
"Since the safety of our guests and employees in our number one priority, the ride has been closed pending further investigation," the theme park said in a statement.
Six Flags Over Texas spokeswoman Sharon Parker said the park is committed to determining exactly what happened.
"It would be a disservice to the family to speculate regarding what transpired," she said. "When we have new information to provide, we will do so."
The Texas Giant was originally designed in 1990 as an all-wooden roller coaster. It was redesigned with a steel track and reopened in April 2011 to mark the theme park's 50th anniversary.
At its highest point, the roller coaster is 153 feet and has a drop of 147 feet, according to the theme park.