Past placental abruption and chance of it happening again?

I'm asking because my good friend lost her son at 23 weeks and it was absolutely one of the most heartbreaking things I've ever witnessed. 
She was having lots of pain and her doc wrote it off as "Braxton hicks" so she went and napped on the couch just to be woken by a severe cramp and as she went to get up, her water broke. 
She barely made it to the hospital before delivering a 1 pound baby. 
He lived for 2 days and passed away due to complications. 
They determined the cause of her going into preterm labor was placental abruption. 
She is now pregnant again and is about 15 weeks along and I'm wondering what are the chances of this happening again? I'm so scared for her :(