Bai Su was reborn. The first thing she did was flee her wedding, because the person she had been betrothed to was a sickly invalid who would die on their wedding night. The emperor would then fly into a rage and demand that she be buried alive with them.
Jing Mo transmigrated into a book. The first thing she did was flee her wedding, because she had transmigrated into the sickly invalid who was destined to die at the very beginning of the story. The moment she breathed her last, a whole group of people would be condemned to die with her in the emperor's fury.
As it happened, they spotted the person they had fled from among the troops guarding the border...
The valiant Bai Su: Hah, a sickly invalid!
The frail Jing Mo: What a match made in heaven!
Years later, the two women who had sworn they would rather die than go through with their weddings: Hey, this is actually pretty great!