Von der Leyen turned out to be dud, so that meant that Merkel either had to run for another term or risk turning the party and the country over to someone who's not loyal to her, like Jens Spahn. She decided to do the former and eventually appointed Annegret Kramp-Karrenbauer as her new heir-apparent after the 2017 election. In picking Kramp-Karrenbauer she even followed the same pattern she had used when appointing Von der Leyen four years prior... choosing a pragmatic, moderate-to-liberal, female CDU politician who's practically a younger clone of yourself.
And AKK has turned out to be a dud as well. Guess this means Merkel will have to run again in 2021...