Caitlin was a test tube baby created by scientists studying cryokenisis, she was the lone survivor of the testing and then labs decided to allow her to live a normal life.

Her 'parents' weren't even married, but they were dating when they first started her new life. When her 'dad' decided to return to the labs, he faked his death and left Caitlin's life.

It's why Killer Frost has been apart of Caits life since she was a child.