Caro had chances to win both sets against Kerber in Copenhagen this year.
When her serve's not working, she has to hit more 2nd serves. And while her 2nd serve is greatly improved, it still means that she's more on the defensive from the get go, and it seems to affect the rest of her play. When her serve is on, she gets easier 2nd shots and you can clearly see her move up the court and put pressure on her opponent. It seems to put her into a more aggressive frame of mind.