Janina Grabowska was taken ill on Friday and Jordan flew out to Poland to see her yesterday (October 21) and will miss this week's rehearsals, The Sun reports.
"It is devastating news for Ola. Her mum is out of the woods but it has been a huge shock for the family," a source told the newspaper.
"She was a real trooper agreeing to dance on Saturday night with that at the front of her mind. We've told her to take as long as she needs."
Sid Owen, Jordan's partner, will rehearse with Iveta Lukosiute, who previously partnered Johnny Ball before he became the first star to be eliminated from the show.
Lukosiute had been drafted in to dance with Ball after his original partner Aliona Vilani suffered an ankle injury.
Singer Dionne Warwick was taken to hospital after recording her performance for the dancing show at the weekend, having previously suffered an ankle injury at her hotel.
Meanwhile, 84-year-old host Bruce Forsyth will miss the November 10 show to rest ahead of the live Children in Need episode from Wembley Arena.
Strictly Come Dancing show four - photo gallery: