Chelsea’s pregnancy was at full term when her waters broke and she went to the Queen Elizabeth University Hospital in Glasgow.
She was checked over and told to go home.
Lorna, who is married to Chelsea’s brother Steven, said her contractions then came on quickly.
Chelsea went back to the hospital ward with her partner Jack and her mum, where it was confirmed she was in labour.
“She was in labour pain but she was still in good spirits and cracking jokes,” Lorna said.
But she said when Chelsea was moved to the bed ready to give birth, she “crashed”.
The midwife raised the alarm and emergency teams began CPR immediately.
Lorna said: “They thought she was maybe panicking and couldn’t catch her breath.
“She was talking one minute then the next, she wasn’t.”
All of Chelsea’s prenatal tests had been normal and the family said she had no underlying health conditions.
“She wasn’t unwell – there were no signs of this,” Lorna added.